Collision-induced absorption in Ar–Kr gas mixtures: A molecular dynamics study with new potential and dipole data

Abstract

We have implemented a scheme for classical molecular dynamics simulations of collision-induced absorption. The program has been applied to a gas mixture of argon (Ar) and krypton (Kr). The simulations are compared with accurate quantum dynamical calculations. The comparisons of the absorption coefficients show that classical molecular dynamics is correct within 10% for photon wave numbers up to 220 cm−1 at a temperature of 200 K for this system. At higher temperatures, the agreement is even better. Molecular dynamics accounts for many-body interactions, which, for example, give rise to continuous dimer formation and destruction in the gas. In this way, the method has an advantage compared with bimolecular classical (trajectory) treatments. The calculations are carried out with a new empirical Ar–Kr pair potential. This has been obtained through extensive analysis of experimental thermophysical and transport properties. We also present a new high level ab initio Ar–Kr potential curve for comparison, as well as ab initio interaction-induced dipole curves computed with different methods. In addition, the Ar–Kr polarizability and hyperpolarizability are reported. A comparison of the computed absorption spectra with an experiment taken at 300 K shows satisfactory agreement although a difference in absolute magnitude of 10%–15% persists. This discrepancy we attribute mainly to experimental uncertainty.

Polyatomic radiative association by quasiclassical trajectory calculations: Cross section for the formation of HCN molecules in H + CN collisions

“…efficient solution regardless the size of reactants. Despite the lacking quantum effects, the trajectory based method with a good quality potential energy surface can provide accurate rate constants, spectral properties and also reliable atomic-scale mechanism of molecular collisions [46][47][48][49][50][51][52][53] .…”

“…Besides the cross section, our method also allows us to extract the spectrum of the emission in collisions. By using the Wiener-Khinchin theorem, it can be shown that this spectrum is similar to that is obtained from dipole-dipole auto-correlation function, which is usually used to calculate vibrational spectrum from molecular dynamics simulations [51][52][53] . However, in our case, we calculate a transient (collision induced) vibrational emission spectrum in contrast to the infrared absorption spectrum of stable molecules.…”