On neglecting Coriolis and related couplings in first-principles rovibrational spectroscopy: Considerations of symmetry, accuracy, and simplicity. II. Case studies for H2O isotopologues, H3+, O3, and NH3

János Sarka, Bill Poirier, Viktor Szalay, Attila G. Császár

Research output: Contribution to journalReview articlepeer-review

1 Scopus citations

Abstract

For centuries, it has been known that vibrational and rotational degrees of freedom are in general not separable. Nevertheless, surprisingly little is known about the best strategies for approximately separating these degrees of freedom in practice—even in the case of semirigid molecules, where the separation is most meaningful. There is also some confusion in the literature about the proper way to quantify the magnitude of the Coriolis (i.e., rotation-vibration) coupling in rovibrational Hamiltonians or its effect on the rovibrational eigenenergies. In this study, a vibrational-coordinate-independent metric is proposed to quantify the magnitude of the Coriolis contribution to the rovibrational Hamiltonian. The impact of Coriolis coupling on the rovibrational eigenenergies is computed numerically exactly, using both full and various truncated Hamiltonians. The role played by the choice of the vibrational coordinate system—and especially by the choice of “embedding” or body-fixed frame—is examined extensively, both numerically and analytically. This investigation targets several molecular prototypes, all of which serve as important benchmarks for the high-resolution spectroscopic community. Most of these are triatomic molecules, including water (H216O), its deuterated isotopologues (D216O and HD16O), H3+, and ozone (16O3), but the tetratomic ammonia molecule (14NH3) is also investigated. These studies provide important insight into the nature of Coriolis coupling under various circumstances. The findings of this study also have significant practical ramifications, vis-à-vis the use of simplifying numerical approximation techniques in nuclear-motion computations.

Original languageEnglish
Article number119164
JournalSpectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
Volume250
DOIs
StatePublished - Apr 5 2021

Keywords

  • Coriolis coupling
  • Eckart embedding
  • Nuclear motion computations
  • Optimal separation of rotations and vibrations
  • Radau bisector embedding

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