Calculation of vibrational fundamental and overtone band intensities of H2O

Abstract

Vibrational intensities are calculated for the fundamental and overtone transitions of H2O up to approximately 18 000 cm−1. The intensities are determined from a dipole moment function expanded in the three internal bond coordinates. The expansion coefficients are computed ab initio at the second-order Mo/ller–Plesset level of theory with a 6-311G** basis set. Vibrational wave functions are calculated either from a three-dimensional harmonically coupled anharmonic oscillator (HCAO) model which uses Morse oscillators to represent both the stretches and the bend of H2O, or from a variational calculation employing the best available potential energy surface and an exact kinetic energy operator. To obtain the most meaningful vibrational intensities we define dipole moment components using the Eckart embedding. Both the HCAO and the variational intensities agree quite well with the experimental results, which span eight orders of magnitude. From the calculations we predict that it may be possible to detect as yet unobserved vibrational transitions of H2O.

Supercritical water: Local order and molecular dynamics

“…Notice that the contribution of the ν 1 mode at about 3657 cm -1 is not observed because its activity is lower by a factor of 10 compared with that of the ν 3 mode [9]. The integrated intensity of absorption of water at T = 380°C and P = 25 bar in the OH stretching region is about 59 ± 2 km mol -1…”

Single-crystal polarized spectra in the near-infrared region: a local-mode analysis of the spectra of M2MnCl4•2X2O (M = Cs, Rb; X = H, D)

“…As a consequence, the average energy (barycentre) of the observed OH stretch fundamentals in H,O and HOD should be the same. This is very nearly true for water in the gas phase (17,21), and in crystals such as K,SnC14.H20, where the effects of hydrogen bonding are small (22). Comparison of the IR spectra of the more strongly hydrogen-bonded BaCl2,2H,O with its HOD analogue indicates, however, that the OH barycentres are on the average 5 cm-I different (2,3).…”

“…the OH, NH, and CH groups. Several reviews of the subject have appeared (12,13), as well as a number of treatments of the theory for water and other small molecules (14)(15)(16)(17)(18)(19)(20). We have outlined elsewhere (2, 3) its application to water on general sites.…”

Spectroscopic Description of H2O in the su(2) Vibron Model Approximation

“…Initially it was applied to small molecules containing CH bonds (10)(11)(12), and more recently to larger molecules (13)(14)(15)(16)(17). In the case of small molecular systems, e.g., triatomic molecules, it is possible to carry out variational calculations using a discrete variable representation and exact kinetic energy operators, but this is not the case for molecules with more than four atoms (18). Hence the HCAO model represents an attractive alternative for the description of complex molecules, but it is necessary to determine how well this model predicts both energies and intensities.…”