On the determination of C0 (or A0), , and some dark states for symmetric-top molecules from infrared spectra without the need for localized perturbations

High-resolution infrared studies of the ν10, ν11, ν14, and ν18 levels of [1.1.1]propellane

“…Though small in magnitude, it is important due to the close proximity of some of the m 11 and m 14 rotational levels and, as discussed later, the perturbations that it produces allow us to determine the C 0 ground state constant. Except in special cases [20], that parameter is normally unavailable from the fundamental bands of infrared spectra of symmetric tops that do not show evidence of such an interaction. The matrix element for this W 5,À1 term is…”

A new analysis of the ν4(E) rovibrational band of the symmetric top molecule PF3

“…More recently, Maki et al [28] proposed a method using several different combinations without the need for localised perturbations.…”

Assignment and analysis of the rotational spectrum of bromoform enabled by broadband FTMW spectroscopy

“…Determination of axial constants in ground states of symmetric top molecules is normally not possible, although in high-resolution infrared spectroscopy several specialized techniques have been used for this purpose, as recently reviewed in [31]. Pure rotational spectra of molecules with nuclear quadrupole coupling offer another route, providing that the quadrupole tensor contains significant off-diagonal elements.…”