ISSN:
1089-7690
Quelle:
AIP Digital Archive
Thema:
Physik
,
Chemie und Pharmazie
Notizen:
Self-consistent-field (SCF) values are reported for all Cartesian tensor components of the dipole, quadrupole, and octupole moments (μ,aitch-theta,Ω) and polarizabilities α and A of the methanol molecule in its staggered, eclipsed, and three intermediate conformations. The methanol geometry was held rigid except for a single internal rotation angle γ, describing the relative orientation of the methyl rotor and the hydroxyl framework. Three different basis sets were used, including a 110 contracted Gaussian set based on the electrical properties (ELP) basis of Dykstra et al. [Adv. Chem. Phys. 75, 37 (1989), and references therein]. It was found that the tensor components Ωxxx, Ωxyy, Axxx, Axyy, and Ayxy vary as cos 3γ, while the components Ωyyy, Ωyxx, Ayyy, Ayxx, and Axyx vary as sin 3γ. All other components of Ω and A, as well as all components of μ, aitch-theta, show little variation with γ. This dependence was explained using a simple model that treats each property as a sum of a constant, hydroxyl framework contribution and a conformation-dependent, methyl rotor contribution. Torsional averages of these properties were computed from torsional wave functions obtained by diagonalization of the internal axis method (IAM) Hamiltonian.It was found that the large amplitude internal rotation in methanol gives rise to large vibrational effects on the Axxx, Axyy, and Ayxy polarizability components. The conformational dependence of the electrical properties was used to describe the conformational dependence of long-range interactions involving a near-symmetric, nonrigid molecule such as methanol. The leading γ-dependent interaction term was shown to vary as R−8 and R−7 for the induction and dispersion interactions (respectively) between a methanol molecule and a structureless atom. Cartesian tensor expressions are given for the long-range dispersion interaction within second-order perturbation theory, and the leading torsionally dependent interaction is shown to vary as sin3 θ cos 3(φ−γ), where θ,φ are the spherical coordinates of the atom.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1063/1.467822
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