Full State-Resolved Energy Gain Profiles of CO2 (J=2-80) from Collisions of Highly Vibrationally Excited Molecules. 1. Relaxation of Pyrazine (E=37900 cm-1)

State-resolved energy gain profiles for strong and weak collisions of pyrazine (E = 37900 cm(-1)) and CO2 are reported. Nascent energy profiles for scattered CO2 (00(0)0, J = 2-64) were measured using high-resolution transient IR absorption spectroscopy at lambda = 2.7 mu m. The data are combined with earlier data for CO2 (J = 58-80) to yield the full State-resolved distribution of scattered CO2 (00(0)0). The scattered CO2 (00(0)0, J = 2-80) molecules have a biexponential rotational distribution with T-lowJ = 437 50 K for J < 50 and T-highJ = 1145 +/- 110 K for J > 50. Fitting the data with a two-component exponential model yields CO2 product distributions with T-rot = 329 and 1241 K. The Cooler distribution accounts for 78% of the scattered population and results front elastic or weakly inelastic collisions that induce very little rotational excitation in CO2. The hotter distribution involves large changes in CO2 rotational energy and accounts for 22% of collisions. The relative translational energy of the scattered molecules increases as a function of final CO2 rotational state with T-rel = 860 K for J = 2 1650 K for J = 60, and 5500 K for J = 80. The total rate constant for appearance of scattered CO2 (00(0)0) is k(app) = (4.8 +/- 1.4) x 10(-10) cm(3) molecule(-1) s(-1), which is similar to 85% of the Lennard-Jones collision rate. Population depletion measurements yield a collision rate of k(dep) = (5.7 +/- 1.8) x 10(-10) cm(3) molecule(-1) s(-1), which is in very good agreement with the Lennard-Jones collision rate. The full energy transfer probability distribution function P(Delta E) for pyrazine(E)-CO2 Collisions is presented and compared to results from other studies.