A theoretical anharmonic study of the infrared absorption spectraof F H F − , F D F − , O H F − , and O D F − anions

• Published in: The Journal of chemical physics 2006-05, Vol.124 (17), p.174308-174308-12
• Main Authors: Elghobashi, Nadia, González, Leticia
• Format: Article
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.2191042

Anharmonic vibrational frequencies, equilibrium bond lengths, rotational constants, and vibrational absorption spectra have been calculated for the triatomic anions, F H F − and O H F − , and the heavier isotopomers F D F − and O D F − . The triatomic anions are assumed to maintain a collinear configuration throughout all calculations, so only the symmetric ( ν 1 ) and asymmetric ( ν 3 ) stretching modes are considered. The two-dimensional permanent dipole surfaces and potential energy surfaces are then constructed along bond coordinates, using high-level ab initio methods. Fundamental and combination bands are obtained from the vibrational eigenfunctions, resulting in anharmonic frequencies, which can be compared with the available theoretical and experimental data. The agreement is very good, especially for the pure symmetric modes, while the asymmetric ones show larger discrepancies, presumably due to the neglected coupling between stretching and bending modes. Strong inverse anharmonicity is found in the level spacing of the asymmetric modes, for both F H F − and O H F − anions. The calculated mixed modes ( n ν 1 + m ν 3 , n , m = 0 - 3 ) also agree reasonably with the few available experimental data, supporting our model. Based on the vibrational eigenfunctions, isotope effects are also rationalized. Infrared absorption spectra are calculated from the dipole autocorrelation function for F H F − and F D F − , and for O H F − and O D F − . Peak locations and relative intensities are assigned in terms of the fundamental and mixed transitions.