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A study was conducted to investigate the effect of alkylation on the strong collisional energy transfer between C[O.sub.2] and a series of highly vibrationally excited alkyl pyridines where alkyl = methyl, ethyl, and propyl. The results have shown that the alkylated donors have undergone strong collision with C[O.sub.2] via a less repulsive part of the intermolecular potential than does pyridine.

Classical trajectory calculations are performed to simulate state-resolved energy transfer experiments of highly vibrationally excited pyrazine and CO2, which are conducted using a high-resolution transient infrared absorption spectrometer. The goal is to use classical trajectories to simulate the supercollision energy transfer pathway wherein large amounts of energy are transferred in single collisions in order to compare with experimental results.

A new approach is described for measuring absolute rates for molecular collisions along with contributions of strong and weak collisions. The method is used for the collisional relaxation of highly vibrationally excited pyrazine with HOD and the observed collision rate is nearly twice the Lennard-Jones collision rate.

Supercollision relaxation of highly vibrationally excited pyrazine (Evib=37 900 cm-1) with D35Cl is investigated using high-resolution transient IR diode laser absorption spectroscopy at 4.4 μm. Highly excited pyrazine is prepared by pulsed UV excitation at 266 nm, followed by rapid radiationless decay to the ground electronic state. The rotational energy distribution of the scattered DCl (v=0,J) molecules with J=15–21 is characterized by Trot=755±90 K. The relative translational energy increases as a function of rotational quantum number for DCl with Trel=710±190 K for J=15 and Trel=1270±240 K for J=21. The average change in recoil velocity correlates with the change in rotational angular momentum quantum number and highlights the role of angular momentum in energy gain partitioning. The integrated energy-transfer rate for appearance of DCl (v=0,J=15–21) is k2int=7.1×10-11 cm3 molecule-1 s-1, approximately one-eighth the Lennard-Jones collision rate. The results are compared to earlier energy gain measurements of CO2 and H2O. [ABSTRACT FROM AUTHOR]

The state-resolved measurements are used for studying the weak and strong collisions between HOD and highly vibrationally excited pyrazine ([E.sub.vib] = 37 900 [cm.sup.-1]). The results have shown that water is an efficient quencher because of a large collisional energy transfer cross section and not due to a large supercollision tail.