Quasi-Classical Trajectory Simulations of Intramolecular Vibrational Energy Redistribution in HONO₂ and DONO₂

Abstract

By use of an analytic potential energy surface developed in this work for nitric acid, the quasi-classical trajectory method was used to simulate intramolecular vibrational energy redistribution (IVR). A method was developed for monitoring the average vibrational energy in the OH (or OD) mode that uses the mean-square displacement of the bond length calculated during the trajectories. This method is effective for both rotating and nonrotating molecules. The calculated IVR time constant for HONO(2) decreases exponentially with increasing excitation energy, is almost independent of rotational temperature, and is in excellent agreement with the experimental determination (Bingemann, D.; Gorman, M. P.; King, A. M.; Crim, F. F. J. Chem.Phys. 1997, 107, 661). In DONO(2), the IVR time constants show more complicated behavior with increasing excitation energy, apparently due to 2:1 Fermi-resonance coupling with lower frequency modes. This effect should be measurable in experiments.

Classical, quantum and statistical simulations of vibrationally excited HOSO2: IVR, dissociation, and implications for OH + SO2kinetics at high pressures

“…The corresponding values of k IVR derived from least squares fits are shown in Table 5, and the results obtained for S replaced by N are in reasonable agreement with the results obtained by Barker and co-workers. 12 The differences between k IVR obtained in our work and theirs likely due to the fact that our PES, optimized for HOSO 2 , is different from their HONO 2 PES. Nevertheless, our results show that the energy in the O-H stretch decays the fastest with nitrogen as the central atom, and slowest with selenium.…”

“…The IVR time constants calculated in this work suggest that OH excitation within the HOSO 2 complex is longer lived than it is in the HONO 2 complex. 12 We investigated the extent to which the difference in the time constants depends on the mass of the sulfur atom. Using the same analytic potential energy surface, the mass of the sulfur atom was changed to that of nitrogren and selenium.…”

“…The calculations performed by Blitz et al assume that the system is ergodic, and that the energy has been completely randomized prior to the dissociation event. Barker and co-workers 11,12 have shown this not to be the case for the redissociation of HONO 2 . The fact that sulfur is more massive than nitrogen suggests that IVR in HOSO 2 may be even slower due to a heavy atom effect.…”

“…13 Thus, the ME RRKM calculations of Blitz et al, 3 where they require very fast IVR for their analysis, may be at odds with the recent results of Barker and co-workers. 11,12 The context for the work presented herein is then twofold: specifically, it is an investigation into the validity of using the proxy method for OH + SO 2 ; and more generally, this work continues from the work of Barker and co-workers 11,12 in order to examine the dynamics of vibrational deactivation, and the appropriateness of statistical approximations for obtaining k N .…”

Isotope dependent, temperature regulated, energy repartitioning in a low-barrier, short-strong hydrogen bonded cluster

“…Energy redistribution in chemical systems has been well-studied [56][57][58][59][60][61][62][63][64][65][66][67][68] in the past few decades. Influenced by the early work of Fermi, Pasta and Ulam 56,63 , three of the present authors 31,69 formulated a scheme to decompose and assign the finite temperature vibrational density of states utilizing harmonic normal mode vectors that are obtained by diagonalizing the nuclear Hessian matrix at minimum energy.…”