Application of the Symmetric Top Approximation to Spectroscopy of High-Temperature Water Vapor

A new model for calculating the energies of pure rotational levels of water vapor molecules treated as a symmetric top is suggested for large values of the quantum number K _a J/2 >> 1. The effective rotational constants of model representation (using the Padé form) of the ground vibrational state of the H₂O molecule are determined. The results of calculations of the rotational line intensities and positions of line centers for the suggested model are preliminarily tested with the help of the information system HOTGAS. The contribution of transitions between high rotational states to the water vapor absorption at temperatures between 1000 and 10000 K is estimated for the 8–12 m wavelength range.