Quasiclassical description of rotational transitions in molecules of asymmetric-top type

The rotational Hamiltonian in action-angle variables is written down for the water molecule considered as a rigid asymmetric top. A method for parametrizing multidimensional potential surfaces is proposed. Quasiclassical quantization of the Hamiltonian, based on the Bohr-Sommerfeld principle, is carried out. Analytic formulas for the cross sections for excitation of rotational levels of the H2O molecule in collisions with atoms are derived by the quasiclassical Dubrovskii-Bogdanov T-matrix method. The rotational excitation constants for a number of rotational levels in the H2O + He system are calculated over a broad temperature range. The results are compared with those of calculations based on the close-coupling method