The overtone spectra of dichloromethane, dibromomethane, and di-iodomethane are measured in the spectral region from 1770 to 850 mμ. The spectra in this region, and the CH stretching fundamentals, are analyzed in terms of a local mode picture. The spectra display the splittings predicted between the symmetrized combinations of local mode states arising from coupling of the two CH oscillators. We calculate the coupling matrix elements directly using a ’’ladder’’ approximation based on the properties of harmonic oscillator wave functions. The validity of this approximation is demonstrated by a comparison to matrix elements of Morse oscillators. Through a direct calculation of the kinetic energy coupling in dichloromethane from the observed bond angle, we show that kinetic energy provides the principal source of coupling in all of these molecules. Differences in overtone spectral structure between the three molecules are attributed to a Fermi resonance involving two quanta of HCH bending. Adiabatic changes in this bending frequency with increased local CH stretching excitation are discussed.

In this paper, we have considered the interplay between phase transitions and configuration mixing of intruder excitations in the [118][119][120][121][122][123][124][125][126][127][128]

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A n investigation of the rotational spectrum of CH,"SH, one of the most recent molecules to be detected in the interstellar medium. has been carried out over the 25-107 GHz region. The frequencies ofci-type Ak = 0 R-branch transitions have been measured for the J = I t O up to J = 4 t 3 multiplets for torsional states c, = 0-3. In addition, many P-, Q -, and R-branch transitions with Ak # 0 have been identified in order to provide a catalogue of lines for potential radio astronomical applications. Improved values of rotational and centrifugal distortion constants, (1-type torsion-vibration-rotation interaction constants, and torsional barrier parameters (V, = 444.76 cm-I; effective V, = -2.07 cm-I) have been determined from least-squares analyses of the spectra.Le spectre de rotation de CH,"SH. I'une des molecules dont la presence a kte tout recemment decelee dans le milieu interstellaire, a i t e etudie dans la region 25-107 GHz. On a mesure les frequences des transitions de type n Ak = Ode la brancheR pour les multiplets J = I + O a J = 4 +-3, pour les etats de torsion I;, = Oa v , = 3. On a de plus identifie plusieurs transitions des branches P, Q et R avec Akf 0, dans le but d'etablir un catalogue de raies pour d'eventuelles applications radio-astronomiques. Des valeurs ameliorkes des constantes rotationnelles et des constantes de distorsion centrifuge, des constantes d'interaction torsion-vibration-rotation et des parametres de barriere torsionnelle (V, = 444,76cm-I; V, effectif = -2 . 0 7~1~-I ) de type n ont kt6 determinkes B partir d'une analyse des spectres par la methode des moindres carres.[Traduit par le journal]Can.