Optical pulse distortion in a grating monochromator

163

Diffusion above a potential barrier under radiative excitation: a model for photochemical reactions in dense phases

BENNY

CARMELI

Department

and

of Chemistry,

ABRAHAM TeC Aviv

NITZAN

University,

Tel Aviv

69978

(Israel)

Kramer’s model for chemical reactions in dense phases, in which the brownian motion of a particle in the presence of a potential barrier is considered, is generalized to include the effect of an incident radiation field. Photochemical reaction rates are derived for simple cases.

General features of coherence effects in spectroscopy

A.A.

VILLAEYS

Centre de Recherches Nucl.@aires et Universitl 67037 Strasbourg C%dex (France) KARL

Louis

Pasteur,

23 rue du Loess,

F. FREED

The James Franck institute and Department Chicago, IL 60637 (U.S.A.)

of Chemistry,

The University

of Chicago,

Recent advances with synchronously pumped dye lasers have enabled a number of research groups to study the role of dephasing processes for coherently excited electronic or vibrational states. Given the presence of well-defined phase relationships, a theoretical description using the coherent state representation more closely approaches the actual experimental situation. In this work we describe general features of the effects of coherence on transient molecular spectroscopy_ A particular emphasis involves the temporal study of the short laser pulses and the resultant near-resonant light scattering produced by these pulses.

Optical pulse distortion in a grating monochromator

R.E.

IMHOF

Department

and D.J.S. BIRCH

of Applied

Physics,

Strathclyde

University,

Glasgow

(Gt. Britain)

Optical pulses are broadened and distorted when passed through a wavelength-dispersive element. The wavelength-dependent pulse shape was calculated for a gaussian pulse dispersed by a rectangular diffraction grating. For a typical

164 grating 100 mm wide and with 1200 lines mm-‘, the pulse broadening can be as large as 0.4 ps nm-‘. The effect is of particular importance in time-resolved experiments with synchrotron sources, such as fluorescence decay and photomultiplier response measurements, where a wavelength-independent pulse shape is often assumed.

State-selectivephotodissociationdynamicsby UV and vacuwn UV laser spe4ztroscopy KARL

H. WELGE

Faku Mt fiir Physik. Universitit Bielefeld, Sielefeld (F.R. G.)

We report photofragment spectroscopy studies with lasers, illustrating the progress in the field. Three experiments are presented: (1) the use of Doppler spectroscopy with a tunable laser (a new version of photofragment spectroscopy) for the first experiments with hydrogen and deuterium detection by tunable Lyman-a laser light; (2) state-selective spectroscopy of molecules in dissociative non-radiative states by multiphoton ionization, e.g. for NO, CD, and CH3 with dissociation lifetimes from leg to lo-l4 s; (3) state-to-state photodissociation with state preparation of the parent molecule in a cold nozzle beam and statespecific analysis of internal and recoil energy and the momentum distribution. Experiments carried out with triatomic molecules, specifically the reaction NO2 + NO + 0, are reported.

Tune-resolved laser spectroscopyof reactionintermediates GEORGE

H. ATKINSON

chemistry Department,

108 Bowne Hdl, Syracuse University, Syracuse, NY

13210 (U.S.A.)

The vibrational mode structures of many short-lived reaction intermediates in room temperature solution have become directly accessible to study through the recent development of time-resolved resonance Raman (TR3) spectroscopy. As a result, intermediates which differ only in their conformations can be readily monitored. These TR3 spectra contain information on both the vibrational modes of the transient species and the kinetic behavior associated with its formation and decay. The use of resonantly enhanced Raman scattering makes it feasible to monitor transient concentrations below lad M and to observe one component