Computing Rovibrational Spectra of Small Polyatomic Molecules with Variational and Collocation Methods

Abstract

It is well-known that some deuterated isotopologues of interstellar molecules achieve a significantly higher deuterium-to-hydrogen ratio than the natural elemental abundance. CH3+ and its deuterated isotopologues are thought to be an important mediator of this process in warm interstellar regions and as such their detection is of interest. To assist in experimental observation, rovibrational calculations have been performed for all isotopologues of CH3+ up to J = 5. Rovibrational levels of CH2D+ and CD2H+ are computed for the first time. Vibrational states up to the 5000-6000 cm-1 range are assigned and their symmetry is determined. The J < 6 levels for the ground, ν1, and ν5 states of CH2D+, and the ground state of CD2H+ compared to observed levels all have a root-mean-square-error (rmse) of less than 0.1 cm-1. The rmse increases to over 0.5 cm-1 for the ν1 mode of CD2H+, thought to be due to a perturbation with another band. Though prior analysis proposes the ν2 +ν 3 overtone as most likely for a perturbing Fermi resonance, these calculations suggest 3ν 3 as the more probable candidate. In addition, the progress on an additional project aimed at supplementing sum-of- products routines is outlined. Preliminary results for P2O look promising, and calculations are presently moving forward on a CH2O example to test the proposed idea.