Study of Hg6(3P0) → Hg6(3P1) excitation induced by collisions with N2, using a double modulation technique

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Abstract
The 253.7 nm emission from N2 + Hg gaseous mixtures at 298 K, illuminated by double modulated 253.7 nm Hg resonance radiation, was measured by means of a photomultiplier coupled to a phase sensitive detector. The emission is composed of a fast and a slow decaying component. Since the 253.7 nm radiation was modulated simultaneously at two different frequencies, at 10 Hz and in the kilohertz region, it was possible to evaluate the fractional intensities of both the fast (DI) and the slow (DII) decaying component of the emission and, in particular, the decay rate (K) of the latter. Imprisonment of the 253.7 nm light affects both the decay rate of the slow decaying component of the emission and the ratio of the intensity of the total emission to that of its fast decaying component. However, the product of these two quantities, K(DI + DII)/DI, is independent of the light imprisonment effects and is directly related to the sum of the pseudo-first-order rate (k5[N2]) of the reaction Hg(3P0) + N2 → Hg(3P1) + N2 (reaction [5]) and of the rate (k′) of the consumption of Hg(3P0) in secondary processes. The latter appears to be very small since the total emission intensity is found to be independent of [N2]. The observed rate constants of the reaction Hg(3P2) + N2 → Hg(3P0) + N2 (reaction [3]) and of reaction [5] at 298 K are k3 = 4.1 × 10−12 and k5 = 2.1 × 10−15 cm3 molecule−1 s−1. The potential uncertainties in these values are estimated to be less than about 15%.

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