Orientation of Asymmetric Top Molecules in a Uniform Electric Field: Calculations for Species without Symmetry Axes

Abstract

Calculations of orientation effects of polar molecules in a uniform electric field are presented for the most general scenario, an asymmetric top molecule with a permanent dipole not parallel to a principal axis. In addition to details of the calculation procedure, including matrix elements of the Hamiltonian, three different treatments of the population distribution of the Stark levels in an electric field are discussed. The adiabatic approach assumes the noncrossing rule for all energy levels as the orientation field increases, the nonadiabatic approach searches for the level with the most similar wave function under field-free conditions to find the population of the Stark level in the field, and the thermal calculation assumes thermal distribution for all of the Stark levels. Among these, the thermal calculation results in the highest degree of orientation, and in high fields, it shows the best agreement with available experimental data in terms of polarization ratios (the ratios of overall excitation...