The interaction of intense picosecond infrared pulses with isolated molecules

Abstract:

In the Past decade there has been much interest in the dynamics of highly vibrationally excited and dissociating molecules. Selectivity at high levels of excitation may eventually lead to the realization of laser-controlled photochemistry, with broad applications in such diverse areas as laser- asisted chemical vapor deposition, isotope separation, and photosythesis. Polyatomic molecules in the ground electronic state can reach levels of excitation up to the dissociation threshold by absorbing a large number of photons from a resonant high-poewr infrared laser. Despite the selectivity of infrared excitation at low energy, however, at high excitation the excitation energy is no longer confined to one 'mode'. It has been shown experimentally that that for molecules excited close to or above the dissociation threshold equilibriation of energy occurs, in agreement with threoretical predictions. There is no agreement, however, as to the validity of theoretical models presuppose equipartitioning of energy in the region below the dissociation threshold. Recent spontaneous Raman spectroscopy experiments on infrared multiphoton excited molecules in our laboratory provide information on the intramolecular vibrational energy distributions of excess of energy can remain in the pumped mode up to levels of excitation close to the dissociation threshold. This paper provides a review of the results that were obtained in the past three years, part of which were published previously.