Treating linear molecule HCCH in calculations of rotation-vibration spectra

• Published in: The Journal of chemical physics Vol. 149; no. 1; pp. 014101 - 14117
• Main Authors: Chubb, Katy L., Yachmenev, Andrey, Tennyson, Jonathan, Yurchenko, Sergei N.
• Format: Journal Article
• Language: English
• Published: United States 07.07.2018
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.5031844

Special treatment is required for ro-vibrational calculations involving polyatomic molecules of linear geometry in order to avoid singularities in the kinetic energy operator. Here we present a variational approach which allows calculations involving such configurations, with a set of 3N–5 linearized coordinates used to represent the vibrations. This approach has been implemented as part of the variational nuclear motion program TROVE (Theoretical ROVibrational Energies). A symmetry adapted basis set based on the Dnh symmetry point group is used. As an illustration of the 3N–5 model presented, TROVE has been used to compute an ab initio room temperature line list for C212H2 using symmetry-adapted ab initio potential energy (CCSD(T)-F12c/cc-pVQZ-F12) and dipole moment surfaces for the ground electronic state. Line positions and intensities (J ≤ 58, l < 8, covering the wavenumbers up to 10 000 cm−1) are compared against HITRAN-2016 and ASD-1000. Alternative methods for treating linear molecules and future work are discussed.