title: Rotational spectrum of SO3 and theoretical evidence for the formation of sixfold rotational energy-level clusters in its vibrational ground state.
abstract: The structure of the purely rotational spectrum of sulphur trioxide (32)S(16)O3 is investigated using a new synthetic line list. The list combines line positions from an empirical model with line intensities determined, in the form of Einstein coefficients, from variationally computed ro-vibrational wavefunctions in conjunction with an ab initio dipole moment surface. The empirical model providing the line positions involves an effective, Watsonian-type rotational Hamiltonian with literature parameter values resulting from least-squares fittings to observed transition frequencies. The formation of so-called 6-fold rotational energy clusters at high rotational excitation are investigated. The SO3 molecule is planar at equilibrium and exhibits a unique type of rotational-energy clustering associated with unusual stabilization axes perpendicular to the S-O bonds. This behaviour is characterized theoretically in the J range from 100-250. The wavefunctions for these cluster states are analysed, and the results are compared to those of a classical analysis in terms of the rotational-energy-surface formalism.
authors.affiliation: Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Underwood
authors.affiliation: Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Sergei N
authors.initials: SN
authors.lastname: Yurchenko
authors.affiliation: Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Tennyson
authors.affiliation: Fachbereich C-Physikalische und Theoretische Chemie, Bergische Universität, D-42097 Wuppertal, Germany.
authors.forename: Per
authors.initials: P
authors.lastname: Jensen