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Journal of Physics B Atomic Molecular and Optical Physics

Quenching of 52P potassium atoms by collisions with H2, N2and CH4

R. W. Berends, W. Kedzierski, A G McConkey, J. B. Atkinson, L. Krause

Published Apr 14, 1989• 6 citations
Publisher

Abstract

Potassium vapour, contained together with a buffer gas in a glass fluorescence cell at a controlled temperature, was irradiated with pulsed dye-laser radiation which excited the K atoms to the 5 2 P 1/2 or 5 2 P 3 / 2 state. The effective decay rate of the 5 2 P atoms was determined in relation to the buffer gas densities by methods of fluorescence spectroscopy with time resolution. The experiments yielded the total quenching (depopulation) cross sections of 19, 94 and 120 AA 2 for collisions with H 2 , N 2 and CH 4 molecules, respectively.

DOI
10.1088/0953-4075/22/7/005

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The transfer of coherence accompanying 42P1/2 → 42P3/2 transfer of excitation induced in collisions between 42P1/2 potassium atoms and noble gas atoms as well as some simple molecules, was studied in a series of sensitized fluorescence experiments. Mixtures of potassium vapor at 6 × 10−7 Torr with the various buffer gases were irradiated with circularly polarized D1(σ+) light and the relative intensities of the σ+ and σ− fractions of both the D1 and D2 fluorescent components were determined in relation to the pressures of the buffer gases. The experiments yielded the following cross sections for coherence transfer: K–He:1.7 Å2; K–Ne :0.8 Å2; K–Ar < 0.5 Å2; K–H2 :3.5 Å2; K–CH4 :7.0 Å2; K–CD4:7.7 Å2.

Canadian Journal of Physics•Feb 15, 1973•6 citations
Potassium vapour, contained together with a buffer gas in a glass fluorescence cell at a controlled temperature, was irradiated with pulsed dye-laser radiation which excited the K atoms to the 5 2 P 1/2 or 5 2 P 3 / 2 state. The effective decay rate of the 5 2 P atoms was determined in relation to the buffer gas densities by methods of fluorescence spectroscopy with time resolution. The experiments yielded the total quenching (depopulation) cross sections of 19, 94 and 120 AA 2 for collisions with H 2 , N 2 and CH 4 molecules, respectively.
Techniques of atomic fluorescence were used to determine cross sections for relaxation and decay of atomic multipole moments associated with the 4 2 P 1/2 and 4 2 P 3/2 states in potassium. 4 2 P 1/2-1/2 or 2 P 3/2-3/2 Zeeman substates were selectively populated by irradiating potassium vapour, mixed with N 2 or H 2 and located in a kilogauss magnetic field, with monochromatic and circularly polarised radiation. Collisions with the buffer gas molecules caused the population of the other Zeeman substates and the emission of a Zeeman fluorescent spectrum, the sigma components of which were resolved with a piezoelectrically scanned Fabry-Perot interferometer. Measurements of the intensities of the Zeeman fluorescent components yielded cross sections for relaxation and decay of the dipole, quadrupole and octupole moments.
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.
Collisions of excited 113Cd(5 3P1) atoms with various molecular gases (N2, H2, D2, CO, CO2, CH4, C2H6, C2H4, O2) have been investigated using atomic fluorescence spectroscopy. By selective excitation of a hyperfine structure level with a pulsed dye laser and studying the time dependence of the fluorescence signals as a function of the buffer gas density the cross sections for quenching, fine structure transfer, and hyperfine structure transfer could be obtained. For N2 molecules the collisions can be described by a decoupling model as has been shown previously for the noble gases as collision partners.
Potassium vapor, contained together with a buffer gas in a fluorescence cell located in a 7-T magnetic field, was irradiated with light from a pulsed dye laser producing selective excitation of the 52{5}^{2}52P1/2{P}_{1/2}P1/2​,-1/2 or the 52{5}^{2}52P3/2{P}_{3/2}P3/2​,-3/2 Zeeman substate. Collisions of the excited and polarized atoms and the resulting Zeeman mixing produced a population of the whole Zeeman manifold and resulted in the emission of a fluorescent Zeeman spectrum which was resolved with a Fabry-Perot interferometer and registered with a photomultiplier and multichannel scaler. Measurements of the relative intensities of the fluorescence components yielded the absolute (thermally averaged) multipole-relaxation cross sections and cross sections for Zeeman mixing by collisions with He, Ne, and Ar atoms.
Collisional excitation transfer and relaxation of K 5sp2\\sp2sp2P atoms in collisions with noble gases, as well as the radiative lifetimes of the K 5P, 6P and 7P fine-structure states have been investigated by methods of atomic fluorescence spectroscopy. Potassium vapour was mixed in a cell with a noble gas and selectively excited by pulsed dye-laser radiation to the 5sp2\\sp2sp2Psb1over2\\sb{1\\over2}sb1over2 or the 5sp2\\sp2sp2Psb3over2\\sb{3\\over 2}sb3over2 state in zero magnetic field and to the 5sp2\\sp2sp2Psb1over2−1over2\\sb{{1\\over 2}-{1\\over 2}}sb1over2−1over2 or the 5sp2\\sp2sp2Psb3over2−3over2\\sb{{3\\over 2}-{3\\over 2}}sb3over2−3over2 Zeeman substate in a field of 70 kG. Interferometric analysis of the fluorescence emitted from the directly (optically) excited state and that emitted from the collisionally populated states allowed the determination of the fine-structure mixing cross sections for collisions with He, Ne, Ar, Kr and Xe in zero magnetic field. Excitation transfer between Zeeman substates was investigated for collisions between the selectively excited 5P atoms and He, Ne and Ar atoms, allowing the determination of the multipole relaxation (depolarization) cross sections for dipole, quadrupole and octupole decay, as well as the Zeeman and fine-structure mixing cross sections and orientation transfer cross sections. A comparison of theoretical calculations with the experimental data has been made and the rate equations governing multipole relaxation and including effects due to strong fine-structure mixing on the multipole relaxation, have been described in detail. The radiative lifetimes of the individual fine-structure components of the K 5P, 6P and 7P states have been determined experimentally by means of time-resolved laser-induced fluorescence techniques. These data are compared with numerous theoretical calculations and the available experimental values.Dept. of Physics. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1988 .B474. Source: Dissertation Abstracts International, Volume: 49-04, Section: B, page: 1223. Thesis (Ph.D.)--University of Windsor (Canada), 1988.
The transfer of coherence accompanying 42P1/2 → 42P3/2 transfer of excitation induced in collisions between 42P1/2 potassium atoms and noble gas atoms as well as some simple molecules, was studied in a series of sensitized fluorescence experiments. Mixtures of potassium vapor at 6 × 10−7 Torr with the various buffer gases were irradiated with circularly polarized D1(σ+) light and the relative intensities of the σ+ and σ− fractions of both the D1 and D2 fluorescent components were determined in relation to the pressures of the buffer gases. The experiments yielded the following cross sections for coherence transfer: K–He:1.7 Å2; K–Ne :0.8 Å2; K–Ar < 0.5 Å2; K–H2 :3.5 Å2; K–CH4 :7.0 Å2; K–CD4:7.7 Å2.