State-to-State, Rotational Energy-Transfer Dynamics in Crossed Supersonic Jets:  A High-Resolution IR Absorption Method

Abstract

A high-resolution IR absorption method is presented for the experimental determination of state-to-state, integral and differential cross sections for rotationally inelastic energy transfer. An infrared chromophore, cooled into its lowest rotational state(s) in a pulsed supersonic expansion, is rotationally excited with low collision probability by a gas pulse from a second supersonic jet. The initial and final populations of the infrared absorber are monitored as a function of J state and of Doppler detuning, via direct absorption of narrow bandwidth light from a continuously tunable, CW infrared laser. The scattered and unscattered species are detected with Doppler-limited spectral resolution (j0.01 cm -1 ), providing quantum-state selectivity not attainable with time-of-flight energy-loss methods. The infrared-based probe also permits study of a much wider class of absorbing species inaccessible to ultraviolet/visible laser-induced fluorescence (LIF) or resonanceenhanced multiphoton ionization (REMPI) methods. From fractional IR absorbances and Beer's law, the column-integrated number densities in each jet are measured directly, which allows absolute, state-to-state, integral cross sections to be determined. Furthermore, the correspondence between the molecular velocity and the observed Doppler shift can be used to extract state-to-state differential cross sections from the highresolution line shapes. Details of the experimental technique are demonstrated via sample studies of stateto-state integral and differential scattering in rare-gas collisions with CH 4 .

State-to-State Inelastic Scattering from S1 Glyoxal with the Rare Gas Series: Uniform Rotational vs Changing Vibrational Channel Competition

“…The motivations for studying rotational transfer with these molecules are often associated with making connections to the interaction PES, and explicit comparisons of the distributions are not given in the literature. Our explorations of the data for CH 4 with He, 32,33 Ne, 33,34 and Ar 33,[35][36][37] show that the situation is much the same as that for the diatomic systems and for glyoxal. The distributions for the heavier rare gases are qualitatively similar, whereas that for He 33 is somewhat distinct.…”

Reactive scattering dynamics in atom+polyatomic systems: F+C2H6→HF(v,J)+C2H5

“…52,53 Thus, only details relevant to the current study will be briefly summarized. Single-collision reaction dynamics are investigated in a 216 L vacuum chamber ͑60ϫ 60ϫ 60 cm 3 ͒, at the intersection region 5 cm downstream of two unskimmed, pulsed supersonic valves oriented at right angles.…”

Time-Resolved O3 Chemical Chain Reaction Kinetics via High-Resolution IR Laser Absorption Methods

“…[21][22][23] Specifically, we have developed an approach based on direct absorption spectroscopy with high-resolution IR lasers, which permits the absolute OH radical density to be probed directly in real time. 24,25 Most importantly, the use of a near IR instead of UV probe allows much higher concentrations of ozone, which provides access to an entirely different regime for study of chemical chain reaction kinetics. The focus of the present work is to describe and apply these high-resolution flash kinetic methods to an investigation of the O 3 /OH/HO 2 chemical chain reaction system under room temperature conditions.…”