This paper provides an overview of the method of single photon ionisation mass
spectrometry. A review of the theory of frequency upconversion using third-order 4-
wave sum mixing in isotropic media and experimental results of third harmonic
generation (THG) using a frequency tripled 355 nm Nd:YAG pump source are
presented. Vacuum Ultra-violet (VUV) photons of wavelength 118 nm are detected in an
acetone ionisation chamber. The emphasis of this paper is on the practical aspects of
generating and detecting the VUV photons and using them for single photon ionisation
(SPI) in the ion source of a mass spectrometer. Optimum gas pressures for THG in Xe
and Xe/Ar mixtures are established. For a pump beam of well defined mode structure the
optimum gas pressures are in excellent agreement with theory. The major loss
mechanism is attributed to re-absorption of VUV by the tripling gas. SPI mass spectra
of hexane and the biomolecule valyl-valine are presented illustrating the power of the
technique.

Nicholas P. Lockyer

John C. Vickerman

Single Photon Ionisation
Mass Spectrometry Using Laser-Generated Vacuum Ultraviolet Photons

The nonlinear optical properties of pseudoisocyanine J-aggregates in Langmuir-Blodgett
films have been investigated by means of degenerate four wave mixing (DFWM) process.
The conversion efficiency of the DFWM signal and the estimated third order
susceptibility were found to be comparable with those of pseudoisocyanine J-aggregates
in solution under comparable resonance conditions. The intensity dependence of the
converted (DFWM) signal is interpreted as resulting from different processes including
saturation, exciton-exciton annihilation and secondary processes of dynamical disorder.

K.-H.  Feller

R.  Gadonas

A.  Pugzlys

D.  M&#246;bius

Near-Resonant Nonlinear Optical
Properties of Pseudoisocyanine J-Aggregates in Langmuir-Blodgett
Layers

We have studied the stability and the structure of doped noble gas cluster ions of the type
M+<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>X</mml:mtext><mml:mi>n</mml:mi></mml:msub></mml:math>, (M=In, Al, Na, X=Ar, Kr, Xe) by systematically changing the composition
M/X and observing changes in the magic number patterns appearing in the mass spectra.
When the metal ion radius is comparable to the radius of the noble gas atom, the mass
spectra show the familar icosahedral magic numbers n+ 1=13,19,23,26,29,32,
46, 55,... In constrast, for metal ions with radii significantly smaller than the noble
gas atoms, we observe a new series of magic numbers n + 9, 11, 17, 21,24, 26,... This
series converts into the icosahedral one for larger clusters. Using a simple hard sphere
packing model, we show that this new series of magic numbers is consistent with a cluster
growth sequence which is based on a capped square antiprism (CSA) geometrical
structure of the clusters.

Christian  L&#252;der

Dimitris  Prekas

Michalis  Velegrakis

Ion-Size Effects in the Growth Sequences of Metal-Ion-Doped Noble
Gas Clusters

Targeting the selective and direct synthesis of tartaric acid (TA), the photochemical
reactions of maleic acid (MA) solutions containing H2O2. in various solvents have been
investigated using four wavelengths in the UV region between 193 and 351 nm, with high
intensity from an excimer laser. All the laser irradiations in H2O resulted in the direct
synthesis of TA with lower selectivity and it was found that, with XeF-laser (351 nm)
irradiation in 1,4-dioxane, TA is selectively and directly synthesized from MA containing
H2O2 of lower concentration at room temperature. On the other hand, none of the
irradiations in methanol, N,N-dimethylformamide, acetonitrile, and tetrahydrofuran
gave the selective formation of TA. On the basis of these results, the reaction scheme for
the selective formation of TA is discussed.

Yuichi Shimizu

Shun&#x27;ichi Sugimoto

Shunichi Kawanishi

Nobutake Suzuki

Laser-Induced Photochemical Reaction of Maleic Acid Solutions in
the Presence of Hydrogen Peroxide

Ablation of thick (&#8776; 15 &#956;m) films of C6H6, C6H5CH3 and C6H5CI at 248 nm and 193 nm
is studied by means of time-of-flight quadrupole mass spectrometry. The dependence of
the desorbate most probable translational energies on laser fluence is determined over the
&#8776;20&#8211;200 mJ/cm2 range. In all cases, the corresponding diagrams are found to exhibit
&#8220;plateaus&#8221;, in accord with the report by Braun and Hess &#91;J. Chem. Phys. 99 (1993) 8330&#93;.
However, no specific correlation with the thermodynamic properties of the compounds is
observed, thereby questioning the attribution of the &#8220;plateaus&#8221; to phase transformation
of the films under ablation conditions. A high sensitivity of the distributions and intensities
on the rate of deposition and the irradiation history of the films is observed,
indicating the importance of the matrix &#8220;structure&#8221; for the distribution of the absorbed
energy. On the other hand, the analysis of the total translational energies of the desorbates
suggests that during ablation, efficient energy transfer occurs in the film. This
possibility is further demonstrated by the observation of high translational energies and
sputtering yields for C6H12(nonabsorbing at 248 nm) condensed in thickness of &#8776; I &#956;m
on top of C6H5CH3 films. These observations can be qualitatively explained in terms of
the collisional sequence model. Alternatively, a photothermal model may be applicable
under the provision that energy distribution in the films is limited due to imperfections
introducing barriers (bottlenecks) to its &#8216;flow&#8217;.

S.  Georgiou

A.  Koubenakis

P.  Kontoleta

M.  Syrrou

A Comparative Study of the
UV Laser Ablation of Van Der Waals Films of Benzene Derivatives

The collisional behaviour of Ba<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>[</mml:mo><mml:mrow><mml:mn>6</mml:mn><mml:mtext>s</mml:mtext><mml:mn>5</mml:mn><mml:mtext>d</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext></mml:mtext><mml:mn>3</mml:mn></mml:msup><mml:msub><mml:mtext>D</mml:mtext><mml:mtext>J</mml:mtext></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow><mml:mo>]</mml:mo></mml:mrow></mml:math>, 1.151 eV above the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>6</mml:mn><mml:mtext>s</mml:mtext><mml:mmultiscripts><mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mmultiscripts><mml:mtext>S</mml:mtext><mml:mprescripts /><mml:none /><mml:mn>1</mml:mn></mml:mmultiscripts><mml:msub><mml:mtext></mml:mtext><mml:mn>0</mml:mn></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow><mml:mprescripts /><mml:none /><mml:mn>2</mml:mn></mml:mmultiscripts></mml:mrow></mml:math> ground state,
is investigated in the presence of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>CH</mml:mtext><mml:mn>3</mml:mn></mml:msub></mml:math>Cl at elevated temperature (900 K) following
the initial pulsed dye-laser excitation of atomic barium via the allowed transition at
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>&#x03BB;</mml:mtext><mml:mo>=</mml:mo><mml:mn>553.5</mml:mn><mml:mtext>nm</mml:mtext><mml:mrow><mml:mo>{</mml:mo><mml:mrow><mml:mtext>Ba</mml:mtext><mml:mrow><mml:mo>[</mml:mo><mml:mrow><mml:mtext>s</mml:mtext><mml:mn>6</mml:mn><mml:mn>6</mml:mn><mml:mtext>p</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext></mml:mtext><mml:mn>1</mml:mn></mml:msup><mml:msub><mml:mtext>P</mml:mtext><mml:mn>1</mml:mn></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow><mml:mo>]</mml:mo></mml:mrow><mml:mo>&#x2190;</mml:mo><mml:mtext>Ba</mml:mtext><mml:mrow><mml:mo>[</mml:mo><mml:mrow><mml:msup><mml:mrow><mml:mn>6</mml:mn><mml:mtext>s</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msup><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext></mml:mtext><mml:mn>1</mml:mn></mml:msup><mml:msub><mml:mtext>S</mml:mtext><mml:mn>0</mml:mn></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow><mml:mo>]</mml:mo></mml:mrow></mml:mrow><mml:mo>}</mml:mo></mml:mrow></mml:mrow></mml:math> in excess helium buffer gas. The optically
mestastable <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>Ba</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext></mml:mtext><mml:mn>3</mml:mn></mml:msup><mml:msub><mml:mtext>D</mml:mtext><mml:mtext>J</mml:mtext></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math> is then subsequently generated in the &#8216;long-time domain&#8217; by a
combination of radiative and collisional processes and may then be monitored b, the
spectroscopic marker atomic emission transition at ,<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>&#x03BB;</mml:mtext><mml:mo>=</mml:mo><mml:mn>791.1</mml:mn><mml:mtext>nm</mml:mtext><mml:mrow><mml:mo>{</mml:mo><mml:mrow><mml:mtext>Ba</mml:mtext><mml:mrow><mml:mo>[</mml:mo><mml:mrow><mml:mn>6</mml:mn><mml:mtext>s</mml:mtext><mml:mn>6</mml:mn><mml:mtext>p</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext></mml:mtext><mml:mn>3</mml:mn></mml:msup><mml:msub><mml:mtext>P</mml:mtext><mml:mn>1</mml:mn></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow><mml:mo>]</mml:mo></mml:mrow><mml:mo>&#x2192;</mml:mo><mml:mtext>Ba</mml:mtext><mml:mrow><mml:mo>[</mml:mo><mml:mrow><mml:mn>6</mml:mn><mml:msup><mml:mtext>s</mml:mtext><mml:mn>2</mml:mn></mml:msup><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext></mml:mtext><mml:mn>1</mml:mn></mml:msup><mml:msub><mml:mtext>S</mml:mtext><mml:mn>0</mml:mn></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow><mml:mo>]</mml:mo></mml:mrow></mml:mrow><mml:mo>}</mml:mo></mml:mrow></mml:math>
 described previously. Following the collision of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>{</mml:mo><mml:mrow><mml:mtext>Ba</mml:mtext><mml:mrow><mml:mo>[</mml:mo><mml:mrow><mml:mtext>6s6d</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext></mml:mtext><mml:mn>3</mml:mn></mml:msup><mml:msub><mml:mtext>D</mml:mtext><mml:mn>1</mml:mn></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow><mml:mo>]</mml:mo></mml:mrow></mml:mrow><mml:mo>}</mml:mo></mml:mrow></mml:math> with
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>CH</mml:mtext><mml:mn>3</mml:mn></mml:msub></mml:math>Cl, the following molecular chemiluminescence transitions of BaCl are also monitored
as a function of time: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>BaCl</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext>A</mml:mtext><mml:mn>2</mml:mn></mml:msup><mml:msub><mml:mo>&#x220F;</mml:mo><mml:mrow><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>&#x2192;</mml:mo><mml:msup><mml:mtext>X</mml:mtext><mml:mn>2</mml:mn></mml:msup><mml:msup><mml:mo>&#x2211;</mml:mo><mml:mo>+</mml:mo></mml:msup><mml:mo>,</mml:mo><mml:mtext>&#x03BB;</mml:mtext><mml:mo>=</mml:mo><mml:mn>966</mml:mn><mml:mtext>nm</mml:mtext><mml:mo>,</mml:mo><mml:mo>&#x25B3;</mml:mo><mml:mtext>v</mml:mtext><mml:mo>=</mml:mo><mml:mn>0</mml:mn></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math>
, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>BaCl</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext>A</mml:mtext><mml:mn>2</mml:mn></mml:msup><mml:msub><mml:mo>&#x220F;</mml:mo><mml:mrow><mml:mn>3</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>&#x2192;</mml:mo><mml:msup><mml:mtext>X</mml:mtext><mml:mn>2</mml:mn></mml:msup><mml:msup><mml:mo>&#x2211;</mml:mo><mml:mo>+</mml:mo></mml:msup><mml:mo>,</mml:mo><mml:mtext>&#x03BB;</mml:mtext><mml:mo>=</mml:mo><mml:mn>910</mml:mn><mml:mtext>nm</mml:mtext><mml:mo>,</mml:mo><mml:mo>&#x25B3;</mml:mo><mml:mtext>v</mml:mtext><mml:mo>=</mml:mo><mml:mn>0</mml:mn></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math>and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>BaCl</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext>B</mml:mtext><mml:mtext>2</mml:mtext></mml:msup><mml:msup><mml:mo>&#x2211;</mml:mo><mml:mo>+</mml:mo></mml:msup><mml:mo>&#x2192;</mml:mo><mml:msup><mml:mtext>X</mml:mtext><mml:mn>2</mml:mn></mml:msup><mml:msup><mml:mo>&#x2211;</mml:mo><mml:mo>+</mml:mo></mml:msup><mml:mo>,</mml:mo><mml:mtext>&#x03BB;</mml:mtext><mml:mo>=</mml:mo><mml:mn>843</mml:mn><mml:mtext>nm</mml:mtext><mml:mo>,</mml:mo><mml:mo>&#x25B3;</mml:mo><mml:mtext>v</mml:mtext><mml:mo>=</mml:mo><mml:mn>0</mml:mn></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math>, the
atomic and molecular profiles all demonstrating exponential decays characterised by
decay coefficients which are equal in given reactant mixtures. It may thus be readily seen
from the kinetic analysis that the three molecule states, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>BaCl</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext>A</mml:mtext><mml:mn>2</mml:mn></mml:msup><mml:msub><mml:mo>&#x220F;</mml:mo><mml:mrow><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn><mml:mo>,</mml:mo><mml:mn>3</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:msup><mml:mtext>B</mml:mtext><mml:mn>2</mml:mn></mml:msup><mml:msup><mml:mo>&#x2211;</mml:mo><mml:mo>+</mml:mo></mml:msup></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math>, are
generated directly on collision of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>Ba</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext></mml:mtext><mml:mn>3</mml:mn></mml:msup><mml:msub><mml:mtext>D</mml:mtext><mml:mtext>J</mml:mtext></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math> with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>CH</mml:mtext><mml:mn>3</mml:mn></mml:msub></mml:math>Cl via exothermic reactions. A
detailed kinetic analysis employing both the integrated intensities of the atomic emission
and these long wavelength molecular emissions, coupled with optical sensitivity calibrations, yields branching ratios in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>BaCl</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext>A</mml:mtext><mml:mn>2</mml:mn></mml:msup><mml:msub><mml:mo>&#x220F;</mml:mo><mml:mrow><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn><mml:mo>,</mml:mo><mml:mn>3</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:msup><mml:mtext>B</mml:mtext><mml:mn>2</mml:mn></mml:msup><mml:msup><mml:mo>&#x2211;</mml:mo><mml:mo>+</mml:mo></mml:msup></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math> states. These are
found to be as follows: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>BaCl</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext>A</mml:mtext><mml:mn>2</mml:mn></mml:msup><mml:msub><mml:mo>&#x220F;</mml:mo><mml:mrow><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mn>4</mml:mn><mml:mo>,</mml:mo><mml:mn>68</mml:mn><mml:mi>&#x0025;</mml:mi><mml:mo>,</mml:mo><mml:mtext>BaCl</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext>A</mml:mtext><mml:mn>2</mml:mn></mml:msup><mml:msub><mml:mo>&#x220F;</mml:mo><mml:mrow><mml:mn>3</mml:mn><mml:mo>/</mml:mo><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mn>1.29</mml:mn><mml:mi>&#x0025;</mml:mi><mml:mo>,</mml:mo><mml:mtext>BaCl</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext>B</mml:mtext><mml:mn>2</mml:mn></mml:msup><mml:msup><mml:mo>&#x2211;</mml:mo><mml:mo>+</mml:mo></mml:msup></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mn>0.24</mml:mn><mml:mi>&#x0025;</mml:mi></mml:math>
The logarithmic variation of these branching ratios with the energies of the states is
essentially Boltzmann in character, with an effective temperature close to the ambient
temperature of the measurements. This is consistent with the absence of propensity in the
yields of these excited molecular states on collision, reflecting the role of late barriers in
the potential surfaces involved.

D.  Husain

Jie  Lei

F.  Castano

M. N. Sanchez Rayo

The Collisional Behaviour of Ba <svg style="vertical-align:-4.8526pt" height="21.887501" version="1.1" viewBox="0 0 78.512497 21.887501" width="78.512497" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"><g transform="matrix(.017,-0,0,-.017,.062,15.775)"><path id="x5B" d="M290 -163h-170v866h170v-28q-79 -7 -94 -19.5t-15 -72.5v-627q0 -59 14.5 -71.5t94.5 -19.5v-28z" /></g><g transform="matrix(.017,-0,0,-.017,5.927,15.775)"><path id="x36" d="M137 343l67 33q37 17 63 17q79 0 129.5 -53t50.5 -131q0 -92 -58 -156.5t-147 -64.5t-147 68t-58 182q0 63 17 119t43 95.5t61.5 72t69 52t67.5 31.5q62 22 128 33l6 -32q-56 -11 -108 -35q-149 -71 -184 -231zM227 337q-47 0 -95 -27q-6 -23 -6 -70q0 -93 36 -155.5&#xA;t96 -62.5q53 0 78 45.5t25 105.5q0 68 -35 116t-99 48z" /></g><g transform="matrix(.017,-0,0,-.017,14.086,15.775)"><path id="x73" d="M319 325l-25 -7q-33 99 -103 99q-29 0 -47 -19.5t-18 -49.5t22 -49.5t62 -36.5q63 -26 95 -57t32 -79q0 -64 -50 -101t-115 -37q-35 0 -67.5 10.5t-46.5 23.5q-5 11 -11 51t-6 67l27 5q14 -53 46.5 -88.5t75.5 -35.5q29 0 50 19.5t21 50.5t-19.5 51.5t-59.5 39.5&#xA;q-28 12 -46 22.5t-38.5 27t-30.5 38.5t-10 49q0 54 42.5 92t109.5 38q48 0 88 -18q6 -15 13 -50.5t9 -55.5z" /></g><g transform="matrix(.017,-0,0,-.017,20.325,15.775)"><path id="x35" d="M153 550l-26 -186q79 31 111 31q90 0 141.5 -51t51.5 -119q0 -93 -89 -166q-85 -69 -173 -71q-32 0 -61.5 11.5t-41.5 23.5q-18 17 -17 34q2 16 22 33q14 9 26 -1q61 -50 124 -50q60 0 93 43.5t33 104.5q0 69 -41.5 110t-121.5 41q-53 0 -102 -20l38 305h286l6 -8&#xA;l-26 -65h-233z" /></g><g transform="matrix(.017,-0,0,-.017,28.484,15.775)"><path id="x64" d="M517 51v-25q-101 -18 -155 -38v65l-61 -36q-50 -29 -78 -29q-68 0 -126.5 58t-58.5 155q0 103 77 175.5t180 72.5q36 0 67 -12v143q0 48 -11.5 58.5t-65.5 14.5v25q79 9 156 34v-597q0 -38 7.5 -48t36.5 -13zM362 85v275q-35 51 -103 51q-20 0 -40.5 -8.5t-42 -28&#xA;t-35 -57.5t-13.5 -89q0 -83 42 -130t96 -47q51 0 96 34z" /></g><g transform="matrix(.017,-0,0,-.017,37.46,15.775)"><path id="x28" d="M300 -147l-18 -23q-106 71 -159 185.5t-53 254.5v1q0 139 53 252.5t159 186.5l18 -24q-74 -62 -115.5 -173.5t-41.5 -242.5q0 -130 41.5 -242.5t115.5 -174.5z" /></g><g transform="matrix(.012,-0,0,-.012,43.338,7.613)"><path id="x33" d="M285 378v-2q65 -13 102 -54.5t37 -97.5q0 -57 -30.5 -104.5t-74 -75t-85.5 -42t-72 -14.5q-31 0 -59.5 11t-40.5 23q-19 18 -16 36q1 16 23 33q13 10 24 0q58 -51 124 -51q55 0 88 40t33 112q0 64 -39 96.5t-88 32.5q-29 0 -64 -11l-6 29q77 25 118 57.5t41 84.5&#xA;q0 45 -26.5 69.5t-68.5 24.5q-67 0 -120 -79l-20 20l43 63q51 56 127 56h1q66 0 107 -37t41 -95q0 -42 -31 -71q-22 -23 -68 -54z" /></g><g transform="matrix(.017,-0,0,-.017,49.675,15.775)"><path id="x44" d="M43 650h280q194 0 282 -85q85 -82 85 -215q0 -173 -123 -267q-107 -83 -297 -83h-236v27q65 5 79.5 19.5t14.5 77.5v402q0 45 -6 62.5t-21.5 24t-57.5 9.5v28zM213 547v-416q0 -55 24.5 -75t81.5 -20q133 0 203 86t70 214q0 80 -30 143t-88 97q-66 41 -170 41&#xA;q-62 0 -78 -13q-13 -9 -13 -57z" /></g><g transform="matrix(.012,-0,0,-.012,62.175,19.863)"><path id="x4A" d="M303 650v-28q-58 -5 -71.5 -19.5t-13.5 -77.5v-373q0 -99 -18.5 -156.5t-67.5 -102.5q-49 -44 -93 -58l-12 29q78 38 96 130q10 60 10 191v340q0 63 -14 77.5t-75 19.5v28h259z" /></g><g transform="matrix(.017,-0,0,-.017,66.712,15.775)"><path id="x29" d="M275 270q0 -296 -211 -440l-19 23q75 62 116.5 174t41.5 243t-42 243t-116 173l19 24q211 -144 211 -440z" /></g><g transform="matrix(.017,-0,0,-.017,72.594,15.775)"><path id="x5D" d="M226 -163h-170v27q79 7 94 20t15 73v627q0 59 -15 72t-94 20v27h170v-866z" /></g></svg> with <svg style="vertical-align:-3.3907pt" height="15.65" version="1.1" viewBox="0 0 30.7875 15.65" width="30.7875" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"><g transform="matrix(.017,-0,0,-.017,.062,11.362)"><path id="x43" d="M614 175l29 -10q-33 -109 -57 -154q-121 -26 -184 -26q-90 0 -160.5 29t-112.5 77t-63.5 105.5t-21.5 119.5q0 157 108 253t277 96q36 0 71.5 -5t69 -13.5t36.5 -8.5q15 -102 20 -150l-29 -8q-20 79 -66.5 114t-128.5 35q-119 0 -187.5 -86t-68.5 -207&#xA;q0 -140 73.5 -227.5t188.5 -87.5q73 0 119.5 37.5t86.5 116.5z" /></g><g transform="matrix(.017,-0,0,-.017,11.367,11.362)"><path id="x48" d="M729 650v-28q-62 -5 -76 -19.5t-14 -75.5v-404q0 -62 13.5 -76t75.5 -19v-28h-268v28q65 5 79.5 19t14.5 76v199h-341v-199q0 -62 14 -76t76 -19v-28h-263v28q61 5 74.5 19t13.5 76v404q0 62 -14 76t-76 19v28h259v-28q-58 -5 -71 -19t-13 -76v-162h341v162&#xA;q0 61 -13.5 75.5t-72.5 19.5v28h261z" /></g><g transform="matrix(.012,-0,0,-.012,24.387,15.45)"><use xlink:href="#x33"/></g></svg> Cl
Investigated by Time-Resolved Atomic Emission and Molecular
Chemiluminescence BaCl <svg style="vertical-align:-5.15417pt" height="22.262501" version="1.1" viewBox="0 0 191.0125 22.262501" width="191.0125" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"><g transform="matrix(.017,-0,0,-.017,.062,15.775)"><use xlink:href="#x28"/></g><g transform="matrix(.017,-0,0,-.017,5.944,15.775)"><path id="x41" d="M673 0h-245v28q47 6 58 16t1 39l-55 154h-213q-31 -87 -36 -129q-16 -47 -5 -61t68 -19v-28h-226v28q50 7 68.5 23.5t43.5 80.5l214 524l24 9l193 -536q23 -63 41.5 -79.5t68.5 -21.5v-28zM418 280l-81 255h-2q-74 -197 -101 -255h184z" /></g><g transform="matrix(.012,-0,0,-.012,17.688,7.613)"><path id="x32" d="M412 140l28 -9q0 -2 -35 -131h-373v23q112 112 161 170q59 70 92 127t33 115q0 63 -31 98t-86 35q-75 0 -137 -93l-22 20l57 81q55 59 135 59q69 0 118.5 -46.5t49.5 -122.5q0 -62 -29.5 -114t-102.5 -130l-141 -149h186q42 0 58.5 10.5t38.5 56.5z" /></g><g transform="matrix(.017,-0,0,-.017,24.025,15.788)"><path id="x220F" d="M851 711q-62 -5 -76.5 -21.5t-14.5 -78.5v-710q0 -63 14.5 -80t73.5 -21v-28h-277v28q63 4 78 21t15 80v761q0 20 -6 25t-27 5h-358q-23 0 -28.5 -5.5t-5.5 -26.5v-759q0 -63 14 -80t72 -21v-28h-268v28q58 4 72 21t14 80v709q0 63 -14.5 79.5t-75.5 21.5v28h798v-28z&#xA;" /></g><g transform="matrix(.012,-0,0,-.012,39.387,20.262)"><path id="x31" d="M384 0h-275v27q67 5 81.5 18.5t14.5 68.5v385q0 38 -7.5 47.5t-40.5 10.5l-48 2v24q85 15 178 52v-521q0 -55 14.5 -68.5t82.5 -18.5v-27z" /></g><g transform="matrix(.012,-0,0,-.012,45.099,20.262)"><path id="x2F" d="M368 703l-264 -866h-60l265 866h59z" /></g><g transform="matrix(.012,-0,0,-.012,50.001,20.262)"><use xlink:href="#x32"/></g><g transform="matrix(.012,-0,0,-.012,55.713,20.262)"><path id="x2C" d="M95 130q31 0 61 -30t30 -78q0 -53 -38 -87.5t-93 -51.5l-11 29q77 31 77 85q0 26 -17.5 43t-44.5 24q-4 0 -8.5 6.5t-4.5 17.5q0 18 15 30t34 12z" /></g><g transform="matrix(.012,-0,0,-.012,58.425,20.262)"><use xlink:href="#x33"/></g><g transform="matrix(.012,-0,0,-.012,64.137,20.262)"><use xlink:href="#x2F"/></g><g transform="matrix(.012,-0,0,-.012,69.039,20.262)"><use xlink:href="#x32"/></g><g transform="matrix(.017,-0,0,-.017,75.375,15.775)"><use xlink:href="#x2C"/></g><g transform="matrix(.017,-0,0,-.017,79.251,15.775)"><path id="x42" d="M372 352v-2q176 -27 176 -159q0 -99 -95 -151q-73 -40 -196 -40h-221v28q65 5 78.5 19t13.5 76v404q0 63 -12 77t-72 18v28h257q102 0 150 -34q26 -18 41 -48.5t15 -65.5q0 -111 -135 -150zM213 362h47q80 0 117.5 32t37.5 96q0 56 -33 92t-100 36q-41 0 -56 -10&#xA;q-13 -8 -13 -50v-196zM213 328v-203q0 -54 17 -72.5t66 -18.5q67 1 110.5 37t43.5 110q0 147 -192 147h-45z" /></g><g transform="matrix(.012,-0,0,-.012,89.25,7.613)"><use xlink:href="#x32"/></g><g transform="matrix(.017,-0,0,-.017,95.588,15.788)"><path id="x2211" d="M697 -46l-42 -182h-602v25l325 457l-308 460v25h585l12 -154l-28 -5q-17 63 -39 88q-12 15 -36.5 20.5t-80.5 5.5h-277l268 -396l-311 -440h382q51 0 75.5 19.5t47.5 83.5z" /></g><g transform="matrix(.012,-0,0,-.012,108.338,7.513)"><path id="x2B" d="M535 230h-212v-233h-58v233h-213v50h213v210h58v-210h212v-50z" /></g><g transform="matrix(.017,-0,0,-.017,123.5,15.775)"><path id="x2192" d="M901 255q-71 -62 -185 -187l-22 15l102 147h-727v50h727l-102 147l22 15q114 -125 185 -187z" /></g><g transform="matrix(.017,-0,0,-.017,147.264,15.775)"><path id="x58" d="M655 0h-263v28q46 5 55.5 14.5t-5.5 34.5l-132 214q-69 -104 -122 -202q-19 -32 -10.5 -43.5t58.5 -17.5v-28h-229v28q44 5 70 17t47 40q47 59 164 239l-134 214q-33 50 -54 64t-74 20v28h246v-28q-44 -5 -52 -14t5 -28q32 -55 114 -182q66 102 99 162q19 33 10.5 44.5&#xA;t-57.5 17.5v28h228v-28q-56 -6 -80 -19.5t-58 -57.5q-45 -62 -121 -179l157 -246q35 -53 60.5 -70t77.5 -22v-28z" /></g><g transform="matrix(.012,-0,0,-.012,158.388,7.613)"><use xlink:href="#x32"/></g><g transform="matrix(.017,-0,0,-.017,164.712,15.788)"><use xlink:href="#x2211"/></g><g transform="matrix(.012,-0,0,-.012,177.462,7.513)"><use xlink:href="#x2B"/></g><g transform="matrix(.017,-0,0,-.017,185.075,15.775)"><use xlink:href="#x29"/></g></svg> Following the Pulsed Dye-Laser Excitation
of Atomic Barium

We shall briefly describe the main research areas, now in progress in our molecular
beam and laser group. The current activity includes our traditional molecular beam
work as well as other experiments carried out in the new labs of our Institute. Essentially
we present here the current progress on Crossed-beam and Beam-gas Chemilumine
scence, Laser-induced Beam Surface Reaction, Laser Analytical Chemistry, Laser-initiated
Reactions Studies by Chemiluminescence and Laser-induced Fluorescence, Spectroscopy
and Structure of van der Waals molecules. For each section recent results are
presented. Due to the basic scope of the present progress report the emphasis is made
on the new experimental developments as well as on the capabilities of both basic and
applied research techniques now operative in our group.

J.  Casta&#241;o

S.  Skowronek

M.  Garay

B.  Besc&#243;s

V.  Zapata

J. M. Orea

A.  Laplaza

G.  Tardajos

R.  Pereira

C.  Rinaldi

A. Gonz&#225;lez Ure&#241;a

Research Activity Using Molecular Beam and Laser Techniques: A Progress Report

The photoionization process of pyrene in non-polar solvent has been investigated using a
two-color two-photon ionization technique. The ionization spectrum near threshold of
pyrene in n-hexane was measured by a delayed
irradiation of a dye laser 20 ns after an N2
laser at total excitation energies of 5.9&#8211;6.22 eV. The two-photon ionization threshold of
pyrene was in the vicinity of 5.9 eV which is larger by 0.7 eV than that expected from the
onset of one-photon ionization. The ionization spectrum shows maxima at 5.92 and 5.99
eV which may be assigned to an autoionization process.

Keiji  Nakashima

Hirofumi  Soga

Teiichiro  Ogawa

Two-Color Two-Photon Ionization Spectrum of Pyrene in N-Hexane

The simultaneous two-photon excitation energy transfer (SEET) was demonstrated for
the first time using trichromophoric model compounds. Two identical donors (A&#8211;antenna)
were covalently linked to an energy acceptor unit (T&#8211;target) with different
energy levels preventing energy transfer of a single photon. At high intensity illumination
(laser exposure) of a trichromophoric system A&#8764;T&#8764;A (A&#8211;fluorescein, erythrosin; T-Estilbene),
sufficient to excite both of the appended donor subunits, population of the
target excited state may occur via simultaneous energy transfer of two photons, one from
each donor. In order to restrict reverse energy transfer from the higher energy target to
the lower energy donor(s) it is necessary that the excited target unit undergoes an
efficient photoreaction. In the investigated case this was achieved by photoisomerization
of the stilbene unit used for monitoring of the SEET.

M.  Nickoleit

A.  Uhl

J.  Bendig

Non-linear Simultaneous Two-Photon Excitation Energy Transfer in
the Wrong Direction

Dispersion of degenerate four-wave mixing (DFWM) efficiency near the exciton resonance
of aggregates of 1,<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mn>1</mml:mn><mml:mo>&#x2032;</mml:mo></mml:msup></mml:math>-diethy1-2-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mn>2</mml:mn><mml:mo>&#x2032;</mml:mo></mml:msup></mml:math>-cyanine (pseudoisocyanine, PIC) chloride is reported.
Correlation with the spectrum of imaginary parts of nonlinearity obtained by pump and
probe techniques is discussed. Third order nonlinear susceptibility of PIC aggregates
has been calculated supposing highest density packing attainable by Langmuir-Blodgett
technique. The nonlinear figure-of-merit of aggregates was evaluated, which is intensity
dependent due to exciton annihilation. Observed intensity and wavelength dependence
of mixing efficiency is qualitatively explained in terms of absorption saturation, exciton
annihilation, and subsequent generation of an excess diagonal disorder by vibrational
energy accumulated in aggregates.

Dispersion of Third Order Optical Nonlinearity of Pseudoisocyanine
J-Aggregates

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Laser Chemistry

Table of Contents

Table of Contents: 1997

Single Photon Ionisation Mass Spectrometry Using Laser-Generated Vacuum Ultraviolet Photons

Near-Resonant Nonlinear Optical Properties of Pseudoisocyanine J-Aggregates in Langmuir-Blodgett Layers

Ion-Size Effects in the Growth Sequences of Metal-Ion-Doped Noble Gas Clusters

Laser-Induced Photochemical Reaction of Maleic Acid Solutions in the Presence of Hydrogen Peroxide

A Comparative Study of the UV Laser Ablation of Van Der Waals Films of Benzene Derivatives

The Collisional Behaviour of Ba with Cl Investigated by Time-Resolved Atomic Emission and Molecular Chemiluminescence BaCl Following the Pulsed Dye-Laser Excitation of Atomic Barium

Research Activity Using Molecular Beam and Laser Techniques: A Progress Report

Two-Color Two-Photon Ionization Spectrum of Pyrene in N-Hexane

Non-linear Simultaneous Two-Photon Excitation Energy Transfer in the Wrong Direction

Dispersion of Third Order Optical Nonlinearity of Pseudoisocyanine J-Aggregates