Counterpropagating Pulsed Molecular Beam Scattering

Abstract

Over the past years great progress has been made in the characterization of molecular processes at the microscopic level.[1] In particular, the dynamics of a variety of photodissociation processes has been studied at the quantum state resolved level.[2] These advances have been made possible through the application of ever more sophisticated laser spectroscopic techniques; often combined with molecular beam techniques.[3] In the study of bimolecular collision processes, progress has been much more difficult to achieve. The main reason is the difficulty in combining laser spectroscopic techniques with the typical crossed beam set-up[4] while at the same time achieving single collision condition and sufficiently high signal levels. These problems are especially severe if angular resolved product distributions are to be detected employing pulsed lasers with inherently low duty cycle. Final state resolved integral cross sections have been determined using infrared absorption[5], laser induced fluorescence[6, 7] or resonance enhanced multiphoton ionization (REMPI).[8, 9] Combining a conventional crossed molecular beam setup with laser induced fluorescence detection. Gentry et al. were able to measure state resolved differential Cross sections for the scattering of NO from Ar.[10] A very elegant method based on Rydberg atom tagging has been developed by Schnieder et al. [11] Its application to the reaction H+H2 and its isotopic variants has demonstrated excellent sensitivity and angular resolution.