On the accuracy of collisional energy transfer parameters for reaction kinetics applications: detailed evaluation of data from direct experiments

Abstract

It is shown that the spread among the various “direct” experimental 〈ΔE〉 data in the literature, so unsatisfactory for their application in chemical kinetics, can be removed consistently. Underlying agreement within very small uncertainties is demonstrated for the case of the much studied collisional relaxation of highly vibrationally excited azulene. Benchmark experimental data for the collisional energy transfer of highly vibrationally excited azulene obtained by the method of “kinetically controlled selective ionization (KCSI)” (U. Hold, T. Lenzer, K. Luther and A. C. Symonds, J. Chem. Phys., 2003, 119, 11 192) are used for a detailed comparison with earlier measurements employing time-resolved ultraviolet absorption (UVA) and infrared fluorescence (IRF). The experimental UVA and IRF traces are simulated by convolution of the transient vibrational distributions g(E) during relaxation obtained from KCSI measurements with the respective calibration curves of the UVA and IRF experiments. The differences between such simulations and the experimental curves are traced back to non-negligible contributions of azulene self-collisions in the UVA and IRF data. Astonishing quantitative agreement is reached when azulene/bath gas mixing ratios of the corresponding UVA/IRF experiments are fully accounted for in the KCSI simulations. The influence of self-collisions is thus quantitatively assessed as an important source of error in addition to the well-known problem of calibration curve uncertainties in UVA and IRF detection as discussed earlier (T. Lenzer, K. Luther, K. Reihs and A. C. Symonds, J. Chem. Phys., 2000, 112, 4090).