Ab initio determination of the roto-torsional energy levels of hydrogen peroxide.

In the present paper, the roto-torsional energy levels of hydrogen peroxide are determined from ab initio calculations performed at the MP4(SDQ)/AUG-cc-pVTZ//MP4(SDQ)/cc-pVTZ+ ++ level. The rotational levels corresponding to the torsional states n = 0 and 1 are determined variationally up to J = 20. The flexible model used considers the roto-vibrational interactions. Symmetry conditions are included for classifying the levels and reducing the cost of diagonalization. Products of contracted torsional basis functions and top symmetric solutions are employed as basis functions. The calculated levels are in a very good agreement with the experimental data. In addition, the K-doubling has been obtained and the levels fitted to the top symmetric equations for determining the centrifugal distortion constants. The expectation values of the rotational constants at the lowest torsional levels are compared with the rotational constants arising from the experimental fit.