Mercury photosensitised luminescence of water vapour
Abstract
The mercury photosensitised luminescence of water vapour is shown to arise from a bimolecular reaction of Hg(63P0) with H2O, by three types of steady-state experiment; no evidence for termolecular reactions has been found.
(1) The emission profile is unchanged as the vapour pressure of H2O is varied between 2 and 600 Torr.
(2) The quantum yields (∼0.25) of the luminescence show little dependence on the total pressure.
(3) By comparing the intensity of the HgH2O* emission to the intensity of the HgNH*3 emission from the same gas mixture, the rate of reaction of Hg(63P0) with H2O is shown to be unaffected when the total pressure is varied from 150 to 600 Torr.
The rate coefficient of the reaction, Hg(63P0)+ H2O = Hg(61S0)+ H2O +hν, was recorded as 1.5(± 0.2)× 10–15 cm3 molecule–1s–1 at 293 K.
The rate of quenching of the 2537 Å line by H2O was found to vary inversely with temperature; it is concluded that the temperature dependent re-excitation of Hg(63P0) to Hg(63P1) is an important process, even at 293 K. It is suggested that the main route for radiationless decay is also a bimolecular reaction of Hg(63P0) with H2O.