Rotation-vibration motion of pyramidal XY3 molecules described in the Eckart frame: Theory and application to NH3

Sergei N. Yurchenko, Miguel Carvajal, Per Jensen, Hai Lin, Jingjing Zheng, Walter Thiel

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49 Scopus citations


We present a new model for the rotation-vibration motion of pyramidal XY3 molecules, based on the Hougen-Bunker-Johns approach. Inversion is treated as a large-amplitude motion, while the small-amplitude vibrations are described by linearized stretching and bending coordinates. The rotation-vibration Schrödinger equation is solved variationally. We report three applications of the model to 14NH3 using an analytic potential function derived from high-level ab initio calculations. These applications address the J = 0 vibrational energies up to 6100cm, the J ≤ 2 energies for the vibrational ground state and the ν2, vν4, and 2ν2 excited vibrational states, and the J ≤ 7 energies for the 4ν2+ vibrational state. We demonstrate that also for four-atomic molecules, theoretical calculations of rotation-vibration energies can be helpful in the interpretation and assignment of experimental, high-resolution rotation-vibration spectra. Our approach incorporates an optimum inherent separation of different types of nuclear motion and thus remains applicable for rotation-vibration states with higher J values where alternative variational treatments are no longer feasible.

Original languageEnglish (US)
Pages (from-to)359-378
Number of pages20
JournalMolecular Physics
Issue number2-3
StatePublished - Jan 20 2005

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