Luminescence of the excited mercury diethylamine complex. Attachment by ligand exchange

Abstract

The possibility of molecular attachment to excited atoms in gases by ligand exchange has been examined. It was first confirmed that mixtures of mercury vapor and diethylamine Et2NH give negligible luminescence when subject to irradiation with the 2537 Å mercury resonance line. The emission was then examined from mercury vapor with added amine up to 100 Torr, in the presence of an excess of NH3. With NH3 alone, a strong emission was observed due to HgNH*3, a complex of Hg(3P0) and NH3, with λmax∼3500 Å. The addition of Et2NH gave rise to a second band to the long wavelength, extending throughout the visible region, with λmax∼5140 Å; the ratio of the intensity of the long wavelength member to the residual emission in the 3500 Å region was found to be proportional to the amine pressure. For various [Et2NH] and fixed [NH3], the set of normalized spectral profiles are isosbestic, corresponding to the superposition of just two basic functions. From the cw experiments, it was adduced that the addition of quite small pressures of Et2NH,∼1 Torr, to NH3 at 1 atm pressure effectively extinguishes the HgNH*3 luminescence by a fast ligand exchange reaction HgNH*3+Et2NH→Hg(Et2NH)*+NH3. The two basic functions which comprise the spectra are due to Hg(Et2NH)* and the dimer Hg(Et2NH)*2, which is the carrier of the long wavelength component. This scheme was confirmed using the resonance flash technique to time resolve the exchange of ligands; the rate coefficient is ∼2×10−10 cm3 molecule−1 s−1 for the above reaction. The radiative lifetime of the Hg(Et2NH)* monomer is 1.15 μs. The large red shift and broadening associated with attachment of the second ligand arises because the emission is from an upper state which belongs to the Hg(3P1) asymptote, and which is more strongly bound than the state which correlates with Hg(3P0).