BROADENING OF H2O ROTATIONAL LINES BY COLLISIONS WITH He ATOMS AT LOW TEMPERATURE

We report pressure broadening (PB) coefficients for the 21 electric-dipole transitions between the eight lowest rotational levels of ortho-H2O and para-H2O molecules by collisions with He at temperatures from 20 to 120 K. These coefficients are derived from recently published experimental state-to-state rate coefficients for H2O:He inelastic collisions, plus an elastic contribution from close coupling calculations. The resulting coefficients are compared to the available experimental data. Mostly due to the elastic contribution, the PB-coefficients differ much from line to line, and increase markedly at low temperature. The present results are meant as a guide for future experiments and astrophysical observations.