Multiphoton dissociation of ketene was studied at 290.5 nm after irradiation of the first
excited singlet state with two different laser pulsewidths of 4 ns and 10 ps. Analysis of the
photofragment fluorescence spectra in the two time domains sheds light on the
mechanisms that are responsible for the production of the observed CH<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext>A</mml:mtext><mml:mtext>2</mml:mtext></mml:msup><mml:mi>&#x0394;</mml:mi></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math>, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mtext>&#x2009;</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:mtext>&#x03A3;</mml:mtext><mml:mo>&#x2212;</mml:mo></mml:msup></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math>
and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>C</mml:mtext><mml:mtext>2</mml:mtext></mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:msup><mml:mtext>d</mml:mtext><mml:mtext>3</mml:mtext></mml:msup><mml:msub><mml:mrow><mml:mtext>&#x03A0;</mml:mtext></mml:mrow><mml:mtext>g</mml:mtext></mml:msub></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:math> photofragments. Multiphoton ionization of cyclohexane induced by a
visible laser at 581 nm and its second harmonic at 290.5 nm was measured in the above
mentioned pulse duration regimes. Study of the dependence of the total ionization signal
on pressure and laser energy helps to clarify the role played by the giant resonance of this
molecule at 84000 cm-1 in the photoionization process.

M.  Castillejo

M.  Mart&#237;n

R.  de Nalda

Nanosecond Versus, Picosecond Molecular Multiphoton Fragmentation of Ketene
and Cyclohexane

A. Gonz&#xE1;lez Ure&#xF1;a

R. J. Donovan

Preface

High resolution Doppler-free laser techniques are used in beam experiments to improve
the spectroscopic description of complex diatomic molecules. The case of TiO is
considered here for its implication in reaction dynamics studies and its interest in
Astrophysics. Two absorption bands in the visible have been analyzed:
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mi>B</mml:mi><mml:mn>3</mml:mn></mml:msup><mml:mtext>&#x03A0;</mml:mtext><mml:mo>&#x2212;</mml:mo><mml:msup><mml:mi>X</mml:mi><mml:mn>3</mml:mn></mml:msup><mml:mtext>&#x2009;</mml:mtext><mml:mi>&#x0394;</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mn>1</mml:mn><mml:mo>&#x2212;</mml:mo><mml:mn>0</mml:mn></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mi>c</mml:mi><mml:mn>1</mml:mn></mml:msup><mml:mtext>&#x03A6;</mml:mtext><mml:mo>&#x2212;</mml:mo><mml:msup><mml:mi>a</mml:mi><mml:mn>1</mml:mn></mml:msup><mml:mtext>&#x2009;</mml:mtext><mml:mi>&#x0394;</mml:mi><mml:mrow><mml:mo>(</mml:mo><mml:mrow><mml:mn>0</mml:mn><mml:mo>&#x2212;</mml:mo><mml:mn>0</mml:mn></mml:mrow><mml:mo>)</mml:mo></mml:mrow></mml:mrow></mml:math>. Owing to accurate wavenumber measurements,
it has been possible to extend the analysis to high rotational quantum numbers
and to carry out detailed spectroscopic calculations. They show that a careful revisiting
of the TiO electronic structure is necessary.

R.  Vetter

P.  Luc

C.  Amiot

High Resolution Spectroscopy With Molecular Beams and Tunable Lasers

A method for the analysis of carbendazim in peper has been developed using
Supercritical Fluid Extraction (SFE) for the sample preparation and the combination
of Laser Desorption (LD) with Resonance Enhanced Multi-Photon Ionization (REMPI)
coupled to Time-of-Flight Mass Spectrometry (TOF-MS) for the detection. The method
allows the analysis of carbendazim in pepper reducing the sample preparation step and
avoiding the matrix effects present in classical GC and HPLC techniques, as well as the
problems related to the labile properties of carbendazim. The detection limit obtained is
of the same order of magnitude as the generally employed HPLC technique, but with
higher sensitivity and easier sample preparation. 

B.  Besc&#243;s

J. M. Orea

C.  Montero

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

A.  Valverde

A.  Aguilera 

Study of Agricultural Samples by Laser Desorption Coupled With Resonance-Enhanced Multiphoton
Ionization and Time-of-Flight Mass Spectrometry: Application to Carbendazim Analysis in Pepper

An overview of recent results obtained by our group on the development of polymeric
solid-state media incorporating either Rhodamine or Coumarin dyes is presented. The
effect on the laser performance of the rigidity and viscoelastic properties of the polymeric
matrix has been investigated. Lasing efficiencies similar to those found in ethanolic
solution, and improved photochemical stability, as compared with that obtained in
previous polymeric materials, were demonstrated for solid solutions of Rhodamine 6G
(Rh6G) in appropriate copolymer formulations of 2-hydroxyethyl methacrylate
(HEMA) and methyl methacrylate (MMA). Further improvements in photostability
were obtained when modified Rh6G molecules were copolymerized with HEMA and
MMA. When samples of this new highly homogeneous gain medium were placed in a
rotating system, where the laser medium was scanned in a continuous way, a stable laser
output with no sign of degradation after 500,000 shots was accomplished for transversal
pumping at 337 nm with 1.7 mJ pulses from a N2-laser at 2 Hz repetition rate. The effect on laser operation of different polymerization methods, dye concentration,
and composition of the polymeric matrix was also investigated for Coumarin-doped gain
media. Conditions were found that significantly improved both lasing efficiency and
photostability in Coumarin 540A (C540A)-doped polymeric matrices. Insight into the
main photodegradation mechanisms of this dye was provided by the study of
fluorescence and lasing properties of a number of C540A solutions with increased
viscosity, from liquid solution to solid polymer matrix.

A.  Costela

I.  Garcia-Moreno

J. M. Figuera

F.  Amat-Guerri

R.  Sastre

Polymeric Matrices for Lasing Dyes: Recent Developments

Pure CF3Br and mixtures of this substance with monoatomic (He, Ar and Xe),
homonuclear diatomic (H2, D2, N2), polyatomic gases (CF4) and NO have been
irradiated with a TEA CO2 laser. Carbon-13 enrichment factor and carbon-13 selectivity
have been estimated from the mass spectrometric analysis of the undissociated CF3Br as
a function of excitation wavelength, fluence, temperature and pressure. The irradiating
wavelength is a crucial parameter to achieve enrichment. The nature of the added gas
also affects considerably selectivity. Best enrichment is achieved in mixtures with NO due
to its radical-like character.

J. I. del Barrio

R. Fern&#225;ndez C&#233;zar

F. M. G.- Tablas

Carbon Isotope Selective Separation From MPD of CF3Br With a TEA CO2 Laser

ZEro Kinetic Energy (ZEKE) spectroscopy relies on electrons produced through delayed
field ionization of the narrow band of high-n Rydberg states which exist just below the
ionization limit of each ionic eigenstate. Using the unique properties of these weakly
bound, stable, high-n Rydberg states (ZEKE states) below the ionization limit rather
than the unbound states above the limit, as in PES, leads to an improvement in
resolution of more than two orders of magnitude. Several different types of ZEKE
experiments, each designed to probe the formation and stability of these states, are
presented here. These experiments were performed with pulsed and static electric fields of
different magnitude and duration at different ion concentrations. The results indicate an
enhanced ZEKE state decay with increasing electric field strengths and an enhanced
formation and stabilization with increasing ion concentrations. A strong interplay
between field strength and ion concentration ZEKE state formation is demonstrated.
The strong influence of electric fields and ion concentrations on the physical properties
of the ZEKE state, above and below the classical ionization threshold, is also
demonstrated through late time (tens of microseconds) decay rate measurements.

A.  Held

E. W. Schlag

The Role of Electric Fields and Ion Concentrations in the Formation and Stabilization of High-n
Rydberg States

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Laser Chemistry | Hindawi

Laser Chemistry

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Laser Chemistry

New Trends in Laser Spectroscopy

New Trends in Laser Spectroscopy

Articles

Nanosecond Versus, Picosecond Molecular Multiphoton Fragmentation of Ketene and Cyclohexane

Preface

High Resolution Spectroscopy With Molecular Beams and Tunable Lasers

Study of Agricultural Samples by Laser Desorption Coupled With Resonance-Enhanced Multiphoton Ionization and Time-of-Flight Mass Spectrometry: Application to Carbendazim Analysis in Pepper

Polymeric Matrices for Lasing Dyes: Recent Developments

Carbon Isotope Selective Separation From MPD of CF₃Br With a TEA CO₂ Laser

The Role of Electric Fields and Ion Concentrations in the Formation and Stabilization of High-n Rydberg States