Abstract :
Some qualitative effects of anharmonicity on the spectra of H3+ and D3+ between low vibrational levels are described. Using large-basis vibration-rotation calculations with a Morse-based discrete variable representation for the vibrations and a symmetric-top basis for the rotations, new spectra of H3+ and D3+ have been assigned. This procedure was assisted by adjusting eight coefficients for H3+ and six coefficients for D3+ in the Meyer-Botschwina-Burton ab initio potential function, and eventually 621 new and old lines of H3+ to levels up to 3ν2 and 529 new and old lines of D3+ to levels up to 2ν2 have been fitted with standard deviations of 0.118 and 0.059 cm−1, respectively. An attempt is made to compare five different potential energy functions for the H3+ system, two ab initio and three adjusted to fit spectra of H3+ or D3+, by expanding them by the same procedure in the same variables. For extension of the present work to higher vibrational levels, more accurate boundary behaviour at linear configurations will be required, and some aspects of the use of hyperspherical coordinates are discussed.
