Probing rotational relaxation in HBr (v=1) using double resonance spectroscopy

Abstract

Rotational energy transfer in HBr(v=1)+HBr collisions has been investigated using an optical pump-probe double resonance technique at ambient temperature. Rotationally state selective excitation of v=1 for rotational levels in the range J=0-9 was achieved by stimulated Raman pumping, and the evolution of population was monitored using (2+1) resonantly enhanced multiphoton ionization spectroscopy of the g (3) summation (-)-X (1) summation (+)(0-1) band. Collision-induced population transfer events with DeltaJ<or=8 were observed at a pressure of 0.32 Torr. State-to-field rate constants for loss of population from the initially prepared states ranged from 8.3x10(-10) to 4.9x10(-10) cm(3) s(-1). The full state-to-state rate constant set was analyzed by fitting to numerical solutions of the coupled differential equations describing the relaxation processes. Rate constant matrices were generated using fitting and scaling functions. The rate coefficients were best represented by the statistical power exponential gap law.

Simultaneous velocity and temperature measurements in gaseous flowfields using the vibrationally excited nitric oxide monitoring technique: a comprehensive study

“…Rotational energy transfer (RET) via collisions between the nascent NO from NO 2 photolysis and bath gas serve to thermalize the rotational distributions. There are several models for state-to-state (J i → J f ) RET cross sections [34,35,36], and optical-optical double resonance experiments have provided direct measurement of these values for specific systems [37,38]. Transitions between small values of ΔJ are efficient, often exceeding the hard-sphere collision rates.…”

State-Specific Collision Dynamics of Molecular Super Rotors with Oriented Angular Momentum

“…Preparing all initial conditions of a molecular collision, including the internal energy and orientation of both collision partners, could lead to reaction efficiencies that approach unity . Significant enhancements in chemical reaction rates are obtained if molecules have added energy in motions that overlap with the reactive coordinate. − A number of schemes have been envisioned to control as many conditions as possible in molecular collisions, including molecular orientation. − The dynamics of nonreactive collisions are affected by the translational, vibrational, and rotational degrees of freedom, leading to a rich variety of observed behaviors. − Because rotational energy states are relatively closely spaced (compared with vibrational and electronic energies), J -changing collisions are common, with many collision systems exhibiting a propensity for small changes in rotational quantum numbers. − Most studies have focused on J -changing collisions within a thermal distribution of states. Here we investigate the rotationally inelastic collisions of molecules in ultrahigh rotational states that are initially prepared with a well-defined plane of rotation and a uniform direction of rotation.…”

Direct determination of state-to-state rotational energy transfer rate constants via a Raman-Raman double resonance technique: ortho-acetylene in v2=1 at 155 K

“…7 In these techniques, the pump process prepares the sample in a well de-fined initial rotational state, while the probe stage monitors the evolution of the population to other rotational states as a function of the delay ͑i.e., the number of collisions͒ between the pump and the probe. Several techniques have been used to prepare the state-selected sample, the most relevant being direct absorption of laser radiation, [8][9][10][11][12][13] the stimulated Raman effect [14][15][16][17] and stimulated emission pumping. 18 The literature shows many combinations of these pump methods with a variety of probe techniques: transient IR absorption, 8,9,13 laser-induced UV 14,19 or IR 8,9 fluorescence ͑LIF͒, resonant enhanced multiphoton ionization ͑REMPI͒, 17,15 coherent anti-Stokes Raman scattering ͑CARS͒, 20 etc.…”