State-to-state rotational relaxation rate constants for the CO+X series (X=CO, He, and Ne) using IR-IR double resonance experiments: comparing theory to experiment

Abstract

ABSTRACT IR-IR double resonance experiments were used to study the state-to-state rotational relaxation of CO with CO, He, and Ne as collision partners. Individual rotational lines of the (2 - 0) vibrational overtone band were pumped by a pulsed IR laser and the subsequent rotational relaxation was monitored using a cw source. The resulting data sets were analyzed by fitting to numerical solutions of the master equation. State-to-state rate constant matrices were generated using fitting law functions. Fitting laws based on the modified exponential gap (MEG) and statistical power exponential gap (SPEG) and energy corrected sudden with exponential power (ECS-EP) models were used. Rate constant matrices for CO+He and CO+Ne were generated from scattering calculations that employed the appropriate ab initio potential energy surfaces. These theoretical rate constant matrices yiel ded kinetic simulations that agreed with the data nearly as well as the fitted MEG model and were unique in their ability to reproduce both the rotational energy transfer and pressure broadening data for CO+He and CO+Ne. Keywords: IR-IR double resonance, state-to-state rotational relaxation