PNNL

Abstract

We present a method to decompose the a-, b- and c- type rotational contours of the gas-phase spectra of asymmetric C1 molecules in which symmetry allows the transition moment projections along any of the three inertial axes, since every vibrational mode transforms with A symmetry. Using the components of the dipole moment derivative along the principal axes of the moment of inertia predicted by modern ab initio computational programs such as Gaussian, in combination with the PGOPHER rotational contour program, the method is able to break down the fraction of the transition moment along each of the three inertial axes and thus predict the rotational contour for each band as a sum of a-, b- and c-type contours. The method is applied to several C1 (and potentially Cs) broadband IR spectra from the Pacific Northwest National Laboratory (PNNL) infrared gas-phase database, showing excellent agreement between predicted and measured spectra.