H216O and H218O maser emission from gas-dust clouds

The collisional pumping of H216O and H218O masers in hot dense gas-dust clouds has been simulated numerically. New data on the rate coefficients for collisional transitions from Faure et al. (2007) were used in the calculations. The possibility of detecting H218O emission in 22.2-GHz H216O maser sources is investigated. The medium is shown to become optically thick in the H218O lines for which an inverted level population is observed at H2O column densities of ∼1019–1020 cm−2. A simultaneous observation of H218O emission and H216O maser emission in the same source will allow the physical conditions in the gas-dust cloud to be refined.