The possibility of using fluoro-organic hypofluorites (CF3OF or CF2(OF)2 as a source of atomic fluorine for hydrogen oxidation in the working mixture of HF-chemical lasers, with pulsed CO2-laser
pumping, was proved theoretically and experimentally. The results suggest an increase of the generation
energy due to the chain reaction energy developed in the chemical laser working mixture.

E. B. Aslanidi

N. P. Aslanidi

N. K. Kalandadze

HF-Chemical Laser Based on Hypofluorite (CF3OF or CF2(OF)2)-Containing Mixtures

Multiphoton IR laser induced isomerization and dissociation of (CF3)2C=C=O (FMK) molecules have been studied. The antisymmetric stretch v1 = 2192 cm-1 of C=C=O&#8212;and antisymmetric v16 = 991 cm-1 of C&#8212;C&#8212; bonds were excited by the second- and first harmonics of a pulsed TEA CO2 laser. The dependence of isomerization conversion on laser radiation frequency, fluence, and number of shots was measured. The isomerization channel was predominant compared with dissociation for the conditions ofIR multiphoton excitation under study.The isomerization of FMK by the second&#8211;harmonic radiation of a CO2 laser was proved to beselective with respect to oxygen isotopes. The isomerization product (FMA molecules) was enriched with18O with maximum value of selectivity &#945;(18/16) = 3.9 when FMK molecules were excited at2&#969;las = 2143.8 cm-1.

V. B. Laptev

L. M. Tumanova

E. A. Ryabov

Selective IR Laser Induced Isomerization and Dissociationof BIS (Trifluoromethyl) Ketene Molecules

The photolysis of silane (SiH4) was carried out using the third harmonic of a Nd: YAG laser at 355 nm, ata fixed SiH4 pressure of 350 Torr, varying the laser energy fluence in the range of 30&#8211;300 Jcm-2. The emission spectra indicates that the photofragments formed are SiH2, SiH, Si, H2, and H. The (A1B1-X1A1) transitions at 552.7 nm, 525.3 nm, 505.6 nm, and 484.7 nm of SiH2 are due to a two photon absorption process. The(A2&#916;-X2&#960;) transitions of SiH at 425.9 nm, 418 nm, 414.2 nm, 412.8 nm and 395.6 nm are due to a three photonabsorption process. The brownish white deposit on the cell windows indicates the presence of amorphoussilicon (a:Si-H). The two atomic lines of Si(4s1P0<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>&#x2192;</mml:mo></mml:math> 3p21D2) at 288.1 nm, and (4s3Pj<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>&#x2192;</mml:mo></mml:math> 3P3Pj) at 251.6 nm areobserved. The atomic Si transitions are due to a three photon absorption. We observed seven transitions dueto molecular hydrogen at wavelengths 577.5 nm, 565.5 nm, 534.4 nm, 542.5 nm, 471 nm, 461.7 nm, and 455.4nm. These bands are due to a four photon absorption proc6ss. In addition to the molecular bands we alsoobserved hydrogen atomic lines <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>H</mml:mtext><mml:mi>&#x03B2;</mml:mi></mml:msub></mml:math>, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>H</mml:mtext><mml:mi>&#x03B3;</mml:mi></mml:msub></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>H</mml:mtext><mml:mi>&#x03B4;</mml:mi></mml:msub></mml:math>.

K.  Sentrayan

E.  Haque

A.  Michael

V. S. Kushawaha

Photolysis of SiH4 by the Third Harmonic of a Nd:YAG Laser at 355 NM

By using two independent and different methods, absolute values of the reaction cross-sections have beendetermined for the following chemiluminescent reactions <mml:math display="block" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>Ca</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mn></mml:mn><mml:mn>3</mml:mn></mml:msup><mml:mtext>P</mml:mtext><mml:mo>,</mml:mo><mml:msup><mml:mn></mml:mn><mml:mn>1</mml:mn></mml:msup><mml:mtext>D</mml:mtext></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mrow><mml:mtext>Cl</mml:mtext></mml:mrow><mml:mn>4</mml:mn></mml:msub><mml:mtext>C</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msub><mml:mrow><mml:mtext>CHBr</mml:mtext></mml:mrow><mml:mn>3</mml:mn></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mo>&#x2192;</mml:mo><mml:msup><mml:mrow><mml:mtext>CaX</mml:mtext></mml:mrow><mml:mo>*</mml:mo></mml:msup><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mtext>A,</mml:mtext><mml:mtext>&#x200B;</mml:mtext><mml:mtext>&#x2009;</mml:mtext><mml:mtext>B</mml:mtext></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mtext>X</mml:mtext><mml:mo>=</mml:mo><mml:mtext>Cl,</mml:mtext><mml:mtext>&#x2009;</mml:mtext><mml:mtext>Br</mml:mtext></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mrow><mml:mtext>Cl</mml:mtext></mml:mrow><mml:mn>3</mml:mn></mml:msub><mml:mtext>C</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msub><mml:mrow><mml:mtext>CHBr</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math> and <mml:math display="block" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>Ca</mml:mtext><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mn></mml:mn><mml:mn>1</mml:mn></mml:msup><mml:mtext>D</mml:mtext></mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mo>+</mml:mo><mml:msub><mml:mtext>H</mml:mtext><mml:mn>2</mml:mn></mml:msub><mml:mtext>O</mml:mtext><mml:mo>&#x2192;</mml:mo><mml:msup><mml:mtext>CaOH</mml:mtext><mml:mo>*</mml:mo></mml:msup><mml:mo>+</mml:mo><mml:mtext>H</mml:mtext></mml:math> Both chemiluminescence and laser-induced fluorescence spectra are reported. A comparison with relatedtypes of reactions is also presented.

F.  Fethi

F.  Poblete

E.  Martinez

A. Gonzalez Urena

G.  Taieb

Reaction Cross Sections of Ca (41S, 43P and 31D States) With HalogenatedCompounds and Water

Two colour photon-gated persistent spectral hole-burning via donor-acceptor electron transfer is reportedin systems where the donor: zinc tetraphenylporphyrin (ZnTPP) and the acceptor: vinylbenzylchloridewhere linked to a polystyrene chain. A spectral hole is observed when the sample is irradiatedusing a gating light in addition to the wavelength-selective light. No effect of the gating light has beenobserved for ZnTPP dispersed in polystyrene (PS) even with efficient acceptors. In contrast, the efficiencyof hole formation under two colour excitation is four times larger than that under one colour excitationin ZnTPP-PBCS/PMMA and nearly two times larger in ZnTPP-PBCS/PS.

S.  Salhi

S.  Kulikov

C.  Bied-Charreton

J. P. Galaup

A New Persistent Photon-Gated Spectral Hole-Burning System:Zinc Tetraphenylporphyrin Linked to Polyvinylbenzylchloride-Co-Polystyrene

Multiphoton dissociation processes of vinyl chloride and bromide were studied with a broadband ArFlaser at 193 nm and with a narrowband tunable laser in the region of 212 nm, in the peak and in thethreshold of the absorption band, respectively, for both compounds. Photolysis at 193 nm gives rise tothe corresponding hydrogen halide in the B1&#8721;+ excited state which results in an intense UV emission. However these emissions are absent when photodissociation was performed with the narrow band dyelaser around 212 nm. These results, together with a calculation of the observed spectra, give furthersupport to a mechanism which invokes one-photon resonant absorption of vibrationally hot ground statehydrogen halide as the process which populates the excited B1&#8721;+ state of the fragment.

Mohamed  Oujja

Javier  Ruiz

Rebeca  De Nalda

Marta  Castillejo

HCL(B1&#8721;+) and HBr(B1&#8721;+) Emission From the Ultraviolet Multiphoton Dissociation of Vinyl Chloride and Bromide

The photophysical properties of benzil dissolved in free solution and in solution confined into a singlebead of porous glasses (size &#60; 100 &#956;m) were investigated by femtosecond transient absorption microspectroscopy.In nonpolar solvent, cyclohexane, the rate of conformational change from the skewed to thenear trans-planar form was reduced from 2.2 &#215; 1012s-1 in free solution to 9.1 &#215; 1011s-1 in porous glasses with an average pore diameter of 26 nm. In polar solvent, DMF, however, there was littledifference between the two systems.

Christopher F. Porter

Naoto  Tamai

Hiroshi  Masuhara

Femtosecond Transient Absorption Microspectroscopy of Benzil ConfinedInto a Single Bead of Porous Glass

Quantum beats in transient absorption of PIC-J-aggregates, modelled by a modified 3-level-system arecalculated. Experimental conditions for the possibility of their observation are investigated. The influenceof the temperature dependent phase relaxation on the temporal evolution of quantum beat signals isconsidered.

H.  Glaeske

K.-H.  Feller

E.  Gai&#154;aukas

L.  Kn&#246;ll

Quantum Beats in Transient Spectroscopy of J-Aggregates

Laser ablation mechanism at 248 nm irradiation of polystyrene film was investigated and discussed. Anablation threshold was determined by etch depth measurement and nanosecond photographic observation.Temperature at the threshold was evaluated to be 370&#8451; by using an effective absorption coefficientwhich was confirmed by transmission measurement of the excitation pulse. The temperature was in goodagreement with that of thermal degradation of the polymer, showing that 248 nm ablation of polystyrenewas brought about by a photothermal process. Nanosecond photography upon the ablation could bewell interpreted from the photothermal viewpoint. Moreover, dynamics of excited species revealed bynanosecond time-resolved luminescence measurements was inferred in relation to the ablation.

Yasuyuki  Tsuboi

Shin-Ichi  Sakashita

Koji  Hatanaka

Hiroshi  Fukumura

Photothermal Ablation of Polystyrene Film by 248 NM Excimer Laser Irradiation:a Mechanistic Study by Time-Resolved Measurements

The photodissociation processes that follow the photolysis of phenylsilane with a narrow band laser at212.5 nm were studied by observing photofragment fluorescence spectra in the 200 to 900 nm range.Emission from several excited states of Si atoms was detected together with emissions from the molecularfragments SiH(A2&#8710;) and C2(d3&#8719;g). Si and SiH emissions show a quadratic dependence with laser energy whereas dependence for C2 emission is cubic, indicating the participation of two and three photon processes in the formation of the respective fragments. The emission spectra of the molecular fragmentsprovides information about their internal energy content and allows discussion of the possible channelsresponsible for the appearance of those fragments.

Margarita  Mart&#237;n

Multiphoton Dissociation of Phenylsilane Upon Excitation at 212.5 NM

Using techniques of delayed pulsed-field ionization zero-kinetic-energy (ZEKE) photoelectron spectroscopy,we have resolved spin-orbit structure in the rotational profile of the origin band in the non-resonanttwo-photon threshold photoionization of propyne. Both the rotational and spin-orbit characteristics of thisband are well-simulated by a simple model that assumes the spin-orbit splitting of acetylene cation incombination with the rotational constants of the neutral propyne ground state. This result, combined withvery little evidence for photoionizing transitions terminating on vibronically excited states, suggests that thestructure of the propyne cation structure is very close to that of the neutral ground state and very little alteredby Jahn-Teller distortion.

Hiroshi  Matsui

Yi-Fei  Zhu

Edward R. Grant

High-Resolution Non-Resonant Two-Photon Threshold Photoionization of Propyne

Molecular weight distributions (MWDs) under free radical polymerization initiation by an arbitrarysequence of radiation pulses have been investigated. Analytical expressions enabling to account for influenceof the polymer chains linear termination (for example, inhibition) have been obtained. On the basis of theseexpressions the MWDs generated by pulse-periodic radiation have been investigated theoretically. Thecalculated MWDs for polymerization in the presence of high concentration of retarder have been given andthe influence of the inhibitor burning within the irradiation process on the MWDs character have beenstudied. It has been shown that possibility to employ the PLP method for determination of polymerizationrate constant (kp) depends significantly on the efficiency ofchains linear termination: the PLP method can beconfidently used at &#964; &#62; T (where &#964; is the effective lifetime of growing radicals, T is the pulse irradiation period)and it is doubtful if &#964; &#60; T/3. The expression for specifying of pulses number required for establishment ofpseudostationary polymerization has been obtained for the polymerization at high concentration of retarder.The calculated MWDs for polymerization of MMA are presented.

A. V. Evseev

A. N. Nikitin

Inhibition Effect on Molecular Weight Distribution GeneratedUnder Free Radical Polymerization by Laser Pulses

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Laser Chemistry