Influence of vibrations and rotations of diatomic molecules on their physical properties: II. Refractive index, reactivity and diffusion coefficients

Abstract

The influence of the excitation of vibrational and rotational states of diatomic molecules (H 2 , N 2 , O 2 , NO, OH, CO, CH, HF and HCl) on refractive index, reactivity and transport coefficients was analyzed by using ab initio calculated data on the effective state-specific dipole moment and static polarizability obtained in the preceding paper of the present series. It has been revealed that, for non-polar molecules, the excitation both of vibrational and rotational degrees of freedom increases the averaged polarizability and, as a consequence, the refractive index. Meanwhile, for polar molecules, the effect of molecule excitation is more complex: it can either increase or decrease the refractive index. It was also shown that the excitation of molecules slightly influences the rate constants of barrierless chemical reactions between neutral particles; whereas, for ion-molecule reactions, this effect can be more pronounced. Analysis of the variation of diffusion coefficients, taking into account the effect of molecule excitation both on the collision diameter and on the well depth of intermolecular potential, exhibited that, for non-polar molecules, the effect associated with the change of collision diameter prevails. However, for polar molecules, the effect of the excitation of vibrational states on the well depth of intermolecular potential can compensate or even exceed the decrease of diffusion coefficient due to the averaged collision diameter rise.

Measured relationship between thermodynamic pressure and refractivity for six candidate gases in laser barometry

“…36 and estimated a dependence of 82 × 10 −7 (cm 3 /mol)/K. The dependence has been calculated for optical frequency as 48(1) × 10 −7 (cm 3 /mol)/K by Buldakov et al 62 and for the static limit as 51 × 10 −7 (cm 3 /mol)/K by Sharipov et al 63 We plot literature measurements of nitrogen polarizability in Fig. 5 across a 30 K range.…”

“…They also thank A. Sharipov and B. Loukhovitski at the Central Institute of Aviation Motors, Moscow, for sharing the numbers underlying their graphical presentation of N 2 polarizability in Ref. 63. The authors understanding of window path length errors has benefited from discussions with G. Bartl and R. Schödel at the Physikalisch-Technische Bundesanstalt, Braunschweig; these interactions encouraged them to include Appendix A.…”

Molecular Collision Diameters and Electronic Polarizabilities: Inherent Relationship and Fast Evaluation

“…■ ON THE RECOVERY OF A LENNARD-JONES POTENTIAL Up to this point, we have not mentioned that in order to completely define the Lennard-Jones 12-6 potential, in addition to the collision diameter σ ij , the second parameter is to be set, namely, the potential well depth ε ij . As is known, 14,37 for a pair of nonpolar neutral molecules of i and j types, ε ij can be expressed in terms of the Slater−Kirkwood approximation for dispersion energy of interaction 29 via σ ij , α el i , and α el j as…”

“…Up to this point, we have not mentioned that in order to completely define the Lennard-Jones 12-6 potential, in addition to the collision diameter σ ij , the second parameter is to be set, namely, the potential well depth ε ij . As is known, , for a pair of nonpolar neutral molecules of i and j types, ε ij can be expressed in terms of the Slater–Kirkwood approximation for dispersion energy of interaction via σ ij , α el i , and α el j as where E h is the atomic energy unit (27.211 eV), a 0 is the Bohr radius, and Z i and Z j are the numbers of valence electrons (the number of electrons in the outer subshell of a molecule; for details, see, e.g. , the classical book).…”

“…Generally speaking, electronic polarizability determines the optic and electrostatic characteristics of molecules − and, alongside the collision diameter, is required for the estimation of the gaseous transport coefficients. ,, Polarizability can be measured using molecular beam deflection in an inhomogeneous electric field or via the Stark shift spectroscopy technique . Alternatively, it can be calculated rather accurately by means of conventional quantum chemical methods based on either the energy expansion formalism (finite field approach) or the coupled perturbed Kohn–Sham and Hartree–Fock theories. − As a result, due to a long-term interest from different areas of basic science and applications, a considerable amount of reliable data has been accumulated for molecular polarizabilities. ,− …”