Rotational energy surfaces of molecules exhibiting internal rotation

Journal Article · Mon Aug 15 04:00:00 EDT 1994 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.467652· OSTI ID:7079846

Ortigoso, J; Hougen, J T ^[1]

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1. Molecular Physics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

Rotational energy surfaces [W. G. Harter and C. W. Patterson, J. Chem. Phys. [bold 80], 4241 (1984)] for a molecule with internal rotation are constructed. The study is limited to torsional states at or below the top of the barrier to internal rotation, where the extra (torsional) degree of freedom can be eliminated by expanding eigenvalues of the torsion--[ital K]-rotation Hamiltonian as a Fourier series in the rotational degree of freedom. For acetaldehyde, considered as an example, this corresponds to considering [ital v][sub [ital t]]=0, 1, and 2 (below the barrier) and [ital v][sub [ital t]]=3 (just above the barrier). The rotational energy surfaces are characterized by locating their stationary points (maxima, minima, and saddles) and separatrices. Rather complicated catastrophe histories describing the creation and annihilation of pairs of stationary points as a function of [ital J] are found at moderate [ital J] for given torsional quantum number ([ital v][sub [ital t]]) and symmetry species ([ital A],[ital E]). Trajectories on the rotational energy surface which quantize the action are examined, and changes from rotational to vibrational trajectories caused by changes in the separatrix structure are found as a function of [ital J] for [ital v][sub [ital t]]=2. The concept of a best'' quantization axis for the molecule-fixed component of the total angular momentum is examined from a classical point of view, and it is shown that labeling ambiguities encountered in the literature for torsion--rotation energy levels, calculated numerically in the rho-axis system, can be eliminated by reprojecting basis-set [ital K] values onto an axis passing through an appropriate stationary point on the rotational energy surface.

• OSTI ID: 7079846
• Journal Information: Journal of Chemical Physics; (United States), Journal Name: Journal of Chemical Physics; (United States) Vol. 101:4; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

664100* -- Theory of Electronic Structure of Atoms & Molecules-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
ACETALDEHYDE
ALDEHYDES
EIGENVALUES
ENERGY LEVELS
EXCITED STATES
FOURIER ANALYSIS
HAMILTONIANS
MATHEMATICAL OPERATORS
MOLECULES
ORGANIC COMPOUNDS
QUANTUM OPERATORS
ROTATIONAL STATES
TORSION
TRAJECTORIES