Collisional energy transfer probabilities of highly excited molecules from KCSI.: III.: Azulene:: P(E′,E) and moments of energy transfer for energies up to 40 000 cm-1 via self-calibrating experiments

Complete experimental transition probability density functions P(E-',E) have been determined for collisions between highly vibrationally excited azulene and several bath gases over a wide energy range. This was achieved by applying 2-color kinetically controlled selective ionization (KCSI) [U. Hold, T. Lenzer, K. Luther, K. Reihs, and A. C. Symonds, J. Chem. Phys. 112, 4076 (2000)]. The results are self-calibrating, i.e., independent of any empirical calibration curve, as usually needed in traditional energy transfer experiments like time-resolved ultraviolet absorption or infrared fluorescence. The complete data set can be described by our recently introduced monoexponential 3-parameter P(E-',E) form with a parametric exponent Y in the argument, P(E-',E)proportional toexp[-{(E-E-')/(C-0+C-1.E)}(Y)]. For small colliders (helium, argon, xenon, N-2, and CO2) the P(E-',E) show increased amplitudes in the wings compared to a monoexponential form (Y<1). For larger colliders, the wings of P(E-',E) have an even smaller amplitude (Y>1) than that provided by a monoexponential. Approximate simulations show that the wings of P(E-',E) at amplitudes <1x10(-6) (cm(-1))(-1) have a nearly negligible influence on the population distributions and the net energy transfer. All optimized P(E-',E) representations exhibit a linear energy dependence of the collision parameter alpha(1)(E)=C-0+C-1.E, which also results in an (approximately) linear dependence of and (1/2). The energy transfer parameters presented in this study have benchmark character in certainty and accuracy, e.g., with only 2%-5% uncertainty for our data below 25 000 cm(-1). Deviations of previously reported first moment data from ultraviolet absorption and infrared fluorescence measurements can be traced back to either the influence of azulene self-collisions or well-known uncertainties in calibration curves. (C) 2003 American Institute of Physics.