Laser-Induced Vibrational Fluorescence in Matrix Isolated Molecules

Abstract

The simplest method to study the dynamics of vibrational levels of matrix isolated molecules consists in irradiating the sample with IR light at the proper frequency and monitoring the population of excited levels through the vibrational fluorescence. Provided the emission light is passed through a monochromator or a set of filters a time and wavelength resolved experiment is then performed. The thermal infrared sources radiating a very small energy per wavenumber unit such experiments are typical of those which have been made feasible by the advent of IR lasers. The method requires a good frequency matching between laser lines and absorptions. This situation can be encountered accidentally like in the case of matrix isolated CO and NO and several lines of the frequency doubled CO₂ laser. The availability of IR lasers should allow this kind of experiments to be extended to many systems. The best example is the excitation of the v = 2 level of HCl in Ar using an optical parametric oscillator followed by 2→ 1 and 1 → 0 fluorescence by Wiesenfeld and Moore [1]. An illustration of the possibilities of the method is provided by the study of vibrational energy transfer in matrix isolated CO and NO [2, 3].