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  • Title: Probing OH stretching overtones of CH3OOH through action spectroscopy: Influence of dipole moment dependence on HOOC torsion.
    Author: Matthews J, Martínez-Avilés M, Francisco JS, Sinha A.
    Journal: J Chem Phys; 2008 Aug 21; 129(7):074316. PubMed ID: 19044776.
    Abstract:
    The OH stretching overtones and OH stretch-HOOC torsion combination bands of methyl hydroperoxide are investigated using action spectroscopy initiated through vibrational state selected photodissociation. Our results for the room temperature spectra covering the 2nu(OH)-5nu(OH) regions suggest that the coarse vibrational structures appearing in the spectra can be understood using a simple two-dimensional vibration-torsion model involving the OH stretch and COOH torsion consistent with what has been previously reported. However, investigation of the jet-cooled spectrum for the 2nu(OH) band along with the results of ab initio calculations using coupled cluster methods reveals that the dependence of the transition dipole moment on the HOOC torsion angle cannot be neglected when simulating intensities of OH stretching overtone bands, as has been suggested by earlier room temperature studies. The present results demonstrate that transitions between torsional levels of different symmetries, which arise from the dependence of the dipole moment mu(r,tau) on the torsional angle, contribute significantly to the intensities of the vibrational overtone bands and are important in interpreting the temperature dependence of the spectral band profiles. Contributions from these transitions are largest for the 2nu(OH) and 3nu(OH) levels and fall off gradually for the higher overtones. In addition, results are presented investigating the orbital interactions in CH(3)OOH that influence changes in the HOOC adiabatic torsion potential with increased OH stretching excitation.
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