The role of the long-range tail of the potential in O₂ + N₂ collisional inelastic vibrational energy transfers

Abstract

In the study of non-reactive energy transfer between O and N molecules bearing different vibrationally excited states we have faced the problem of selecting a proper formulation of the interaction. To this end we have compared the values of the related observables computed either on a potential energy surface globally fitted to very large ab initio potential energy values [Varga et al., J. Chem. Phys., 2016, 144, 024310] or on two more traditional ones formulated as a combination of an intra- and inter-molecular model component of the interaction (and based on a different combined use of experimental and ab initio information) [Garcia et al., J. Phys. Chem. A, 2016, 120, 5208] in order to enforce an appropriate modelling of the long-range tail of the potential, crucial for the description of inelastic vibrational energy transfer. A detailed graphical analysis of the potential plus a quantitative analysis of the computed opacity functions, of the state-to-state rate coefficients, of the second virial coefficient and of the integral non-reactive cross section allowed us to conclude that the model formulation of the interaction has to be preferred for non-reactive studies of the O + N energy transfer processes in thermal and subthermal regimes.

Global and Full-Dimensional Potential Energy Surfaces of the N2 + O2 Reaction for Hyperthermal Collisions

“…The DSEC and UCCSD(T)-F12a/AVTZ results show a slight deviation of about 0.2–0.7 kcal mol –1 , while the overall agreement is satisfactory. As can be seen from Figure b,c, the MF2 PES is in good agreement with UCCSD(T)-F12a/AVTZ, consistent with the previous finding that the UCCSD(T)-F12a/AVTZ method is more accurate than the DSEC method for the interaction between rigid N 2 and O 2 . The interactions on the three PESs are slightly different for the long-range interactions.…”

“…As can be seen from Figure 4b,c, the MF2 PES is in good agreement with UCCSD(T)-F12a/AVTZ, consistent with the previous finding that the UCCSD(T)-F12a/AVTZ method is more accurate than the DSEC method for the interaction between rigid N 2 and O 2 . 15 The interactions on the three PESs are slightly different for the long-range interactions. In Figure 4a, for d within 4.0−5.5 Å, the energies by the PIP-NN method are 0.2−1.0 kcal mol −1 higher than those by the MB-PIP and MB-PIP-NN methods.…”

“…For this PES, 54,046 data points were computed at the multi-state complete-active-space second-order perturbation theory (MS-CASPT2) − level with the minimally augmented correlation-consistent polarized valence triple-zeta (maug-cc-pVTZ) basis set. − The energies of these data were then dynamically scaled with the dynamically scaled external correlation (DSEC) method to recover a larger fraction of the external correlation and fitted to the many-body (MB) function form with the four-body component represented by the permutationally invariant polynomial (PIP) in terms of bond-order functions of the six interatomic distances. The resulting PES, abbreviated as the MB-PIP PES, has been widely used for kinetic and dynamic simulations. − The MB-PIP PES played a crucial role in the development of high-temperature aerothermodynamics. Our understanding and prediction ability have been significantly improved, and the simulated results were generally consistent with available experiments.…”

“…14 The quality of the PES determines the reliability of subsequent kinetic and dynamic simulations. Garcia et al 15 pointed out that the MB-PIP PES is not accurate enough for the description of the N 2 + O 2 interaction region, making the results of inelastic collision-related thermodynamic parameters such as the virial coefficient and the integral nonreactive cross-section inaccurate. As we pointed out in the recent book chapter, 25 the quality of the PES depends on the data and sampling, the level of electronic structure calculation, and the PES fitting method.…”

Master equation simulation of O2-N2 collisions on an ab-initio potential energy surface

“…The vibration-translation (VT) and vibration-vibration (VV) energy transfer was studied by a semi-classical coupled method by Billing on an empirical PES in the range of temperatures between 250 and 1000 K. 23 Recently, Garcia et al 37,38 reported VT and VV RCs using an improved PES for selected vibrational states of oxygen at temperatures up to 7000 K. This PES is based on ab-initio calculations that are interpreted as a combination of van der Waals and electrostatic interaction terms. Unfortunately, the dataset reported in Ref.…”