Overtone Bands of H3f: First Principle Calculations

Since its spectrum was first observed by Oka (I) and Shy et al. (2) in 1980, H: and its isotopomers have excited considerable interest among experimental spectroscopists and theoretical chemists alike. All the infrared-allowed fundamentals of the ions have been characterized (3-8). The microwave spectrum of H2D+ has tentatively been observed in the interstellar gas cloud NGC 2264. At the same time, there have been several ab initio studies of Hi (9-11) which have led to attempts to calculate the experimentally observed vibration-rotation spectra from first principles (11-16). Recently, we have undertaken such calculations using a new ab initio surface due to Meyer et al. (17). Initial results for the vibration-rotation spectra of the fundamental bands confirmed the Meyer et al. prediction that their surface would give very good agreement with experiment. In a previous paper (18), henceforth referred to as Paper I, the results for the fundamentals were given in the form of the molecular constants due to Watson (3-8, 19) to facilitate comparison with experiment. The rotational term values for HzD+ (20) DzHf (2I), and D: (22) have also been reported. Despite the intensity of the theoretical and experimental activity, there are features in the infrared spectrum of Hi that have still to be assigned (23). It is believed that these may be due to “hot bands,” transitions from vibrationally excited states to higher energy vibrations, with relatively low values of the angular momentum quantum number, J. It is also possible that the hot band spectrum of H: could be a candidate for astronomical observation in molecular clouds that have been subjected to shocks (24). For these reasons, and because the accuracy of our previous results for the fundamentals gives cause for confidence in our values for higher energy levels, we are presenting here results for the vibrational origins and rotational terms for the overtone bands of H$. We also give rotational terms for the fundamental vibrations in order that the relevant hot band frequencies might be calculated.