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Canadian Journal of Physics

Quenching and Depolarization of Mercury Resonance Radiation

J. S. Deech, John M. Pitre, L. Krause

Published Aug 1, 1971• 60 citations
Publisher

Abstract

The quenching and depolarization of mercury resonance radiation (2537 Å), induced in collisions of Hg(63P1) atoms with various molecules has been investigated using the method of delayed coincidences. The following total quenching cross sections have been obtained for the process Hg(63P1) → Hg(63P0, 61S0): Hg–H2, 24.6 Å2; Hg–D2, 22.7 Å2; Hg–CO, 21.7 Å2; Hg–CO2, 10.2 Å2; Hg–O2, 60.5 Å2; Hg–14N2, 0.73 Å2; Hg–15N2, 0.78 Å2; and Hg–Xe, < 0.002 Å2. A cross section of 267 Å2 has been measured for the depolarization of the resonance radiation by collisions with CO2 molecules.

DOI
10.1139/p71-239

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Canadian Journal of Physics•Nov 15, 1974•12 citations
The quenching and depolarization of mercury resonance radiation (2537 Å), induced in collisions of Hg(63P1) atoms with various molecules has been investigated using the method of delayed coincidences. The following total quenching cross sections have been obtained for the process Hg(63P1) → Hg(63P0, 61S0): Hg–H2, 24.6 Å2; Hg–D2, 22.7 Å2; Hg–CO, 21.7 Å2; Hg–CO2, 10.2 Å2; Hg–O2, 60.5 Å2; Hg–14N2, 0.73 Å2; Hg–15N2, 0.78 Å2; and Hg–Xe, < 0.002 Å2. A cross section of 267 Å2 has been measured for the depolarization of the resonance radiation by collisions with CO2 molecules.
The transfer of excitation from excited mercury atoms to ground-state thallium atoms was investigated using techniques of sensitized fluorescence. A Hg–Tl vapor mixture contained in a quartz cell was irradiated with Hg 2537 Å resonance radiation which caused the mercury atoms to become excited to the 63P1, state. Subsequent collisions between the Hg(63P1) and Tl(62P1/2) atoms resulted in the population of the 82S1/2, 62D, and 72S1/2 thallium states, whose decay gave rise to sensitized fluorescence of wavelengths 3231, 3520, 3776, and 5352 Å. Intensity measurements on the sensitized fluorescence and on the Hg 2537 Å resonance fluorescence, observed at right angles to the direction of excitation, yielded cross sections of 3.0, 0.3, and 0.05 Å2 for collisional excitation transfer from Hg(63P1) to the 82S1/2, 62D, and 72S1/2 states in thallium, respectively. The results are fully consistent with previously determined cross sections for excitation transfer in other binary metallic vapor systems.
The behavior of the sensitized fluorescent spectrum of sodium, produced by irradiating Hg–Na–N2 mixtures with Hg 2537 Å resonance radiation, was studied in relation to N2 pressure. In this ternary vapor-gas system, the sodium atoms become excited by collisional transfer from Hg 63P1 atoms and also from Hg 63P0 atoms which are formed in Hg(63P1) + N2 collisions. The spontaneous decay of the collisionally populated S, P, and D sodium states gives rise to the fluorescent spectrum and their radiationless decay (quenching) caused by collisions with N2 molecules, manifests itself in a decrease of the fluorescent intensities as N2 pressure is increased. An analysis of the variation of the fluorescent intensities with N2 pressure, yielded 15 quenching cross sections for various S, P, and D sodium states, which appear to exhibit resonance properties with respect to upward vibrational transitions in N2.
The effects of imprisonment of resonance radiation in potassium vapor and of collisions between excited potassium atoms and N2, H2, HD, and D2 molecules, on the measured lifetimes of the 42P states, have been investigated by the method of delayed coincidences. The potassium atoms were excited with short pulses of resonance radiation, and the delays between the exciting and fluorescent pulses were measured with a time-to-amplitude converter. At pure potassium densities below 1010 atoms/cm3, the measured lifetimes approach the constant values 27.8 ± 0.8 and 27.6 ± 0.8 ns, corresponding to the natural lifetimes of the 42P1/2 and 42P3/2 states, respectively. At higher densities the effective lifetimes are in satisfactory agreement with the predictions of Holstein's theory. The decrease in the measured decay rates observed upon addition of the diatomic gases yielded cross sections for quenching collisions with N2, H2, HD, and D2 which equal 34.0 ± 2.0 Å2, 9.4 ± 1.3 Å2, 11.9 ± 1.5 Å2, and 8.0 ± 2.0 Å2, respectively.
The cross section for the transition $6^{3}P_{0}\ensuremath{\rightarrow}6^{3}P_{1}$ in mercury, induced in collisions with N2{\mathrm{N}}_{2}N2​ molecules, has been determined by the method of delayed coincidences. The Hg 3P1^{3}P_{1}3P1​ state was excited by pulses of 2537-\AA{} Hg resonance radiation and the decay of the long-lived 2537-\AA{} afterglow was studied in relation to N2{\mathrm{N}}_{2}N2​ pressure. The resulting cross section ${Q}_{12}(^{3}P_{0}\ensuremath{\rightarrow}^{3}P_{1})=4.18\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ A˚2{\mathrm{\AA{}}}^{2}A˚2 was found to be good agreement with the prediction of the principle of detailed balancing when compared with the cross section ${Q}_{21}(^{3}P_{1}\ensuremath{\rightarrow}^{3}P_{0})$. It was also found that, within the sensitivity of the method, collisions with N2{\mathrm{N}}_{2}N2​ molecules do not quench 3P1^{3}P_{1}3P1​ or 3P0^{3}P_{0}3P0​ Hg atoms to the ground state.
The transfer of excitation energy induced in inelastic collisions between excited Hg atoms and ground-state Cd atoms was studied using methods of sensitized fluorescence. Hg atoms in a low-density Hg–Cd vapor mixture were excited with Hg 2537 Å resonance radiation to the 63P1 state and interacted with the Cd atoms which became collisionally excited to the 53P1 state and subsequently decayed emitting sensitized fluorescence. Measurements of relative intensities of Hg 2537 Å resonance fluorescence and Cd 3261 Å sensitized fluorescence yielded the cross section Q(63P1 → 53P1) = 4.6 × 10−2 Å2. The efficiency of the excitation transfer was enhanced by the addition of small quantities of N2 to the Hg–Cd system. The cross section for quenching of the Cd 53P1 state by collisions with N2 was found to be 1.7 Å2.