Calculated intensity in the local mode overtone spectra of hydrogen peroxide

Abstract

Calculations of OH stretching vibrational intensities for hydrogen peroxide are performed with a harmonically coupled anharmonic local mode model for the OH stretching vibrational wave functions and ab initio calculations to obtain the dipole moment function. The ab initio calculations are carried out at three different levels: Self-consistent field (SCF), second-order Mo/ller–Plesset perturbation theory (MP2), and configuration interaction including all single and double excitations (CISD), all with a 6–31G* basis set, to yield the dipole moment function. From these results, total oscillator strengths are calculated for the three different types of rotational bands in a given OH stretching transition. The calculated overtone intensities for ΔvOH=2–5 are not sensitive to the particular dipole moment function. However, a significant decrease in intensity occurs for the fundamental transition in going from the molecular orbital to the correlated level calculations. Our calculated results are compared to near infrared, photoacoustic, and molecular beam experiments by other workers. The calculations can explain many of the experimental results, although the interpretation is not always straightforward. Our calculations suggest that transitions to the symmetric OH stretching mode, should be included in the analysis and assignment of the OH stretching overtone regions.