Measurements of N₂ refractive index and scalar polarizability in a pulsed nanosecond non-equilibrium discharge by Mach–Zehnder interferometry and spontaneous Raman scattering

Abstract

This paper presents quantitative measurements of the N2 Gladstone–Dale constant and scalar polarizability in non-equilibrium conditions, created by a nanosecond pulsed discharge at a pressure of 90 Torr. Optical path differences and spatially varying refractive index profiles are obtained by temporally-resolved Mach–Zehnder interferometry. Spontaneous Raman scattering spectroscopy is used to investigate the highly non-equilibrium vibrational population and to measure the N2() vibrational temperature and rotational temperature in the discharge afterglow region. The local gas density is inferred from the rotational temperature with isobaric conditions at long time delays ranging from 10 to 500 µs after initiating the pulsed discharge. The non-equilibrium effects on the N2 Gladstone–Dale constant and scalar polarizability are reported within a rotational temperature ranging from 300 to 1000 K. To the best of our knowledge, this is the first time the refractivity of gas has been measured under non-equilibrium conditions in a pulsed discharge afterglow.

A simple semiempirical model for the static polarizability of electronically excited atoms and molecules

“…Electric properties of atoms, molecules, and clusters, which have been widely studied over the years, [1][2][3][4] continue to attract the attention of numerous research groups involved in different areas of atomic, molecular, optics, and chemical physics as well as in relevant existing and emerging technological applications. [21,[27][28][29][30][31] This is because the electric properties (primarily, dipole polarizability and, if present, permanent dipole moment) specify the variety of optical [1,32,33] and electrical [9,[34][35][36] phenomena in molecular gases, underlie the theory of infrared and Raman vibrational spectra, [37] play a paramount role in intermolecular [11,19,23,[38][39][40][41] and electron-molecular [42][43][44] interactions, and serve as markers of thermodynamic and kinetic stability of atomic/molecular systems. [24,25,40,[45][46][47][48][49][50][51][52][53] In this respect, it is not surprising that as a result of numerous experimental and theoretical efforts, a vast body of knowledge on the electric properties of atoms, molecules, atomic and molecular clusters has been gathered to date, [6]…”