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Journal of the Optical Society of America

Measurement of excitation cross section of the 6 ^3P_1 state of Hg using self-calibrating apparatus

R. Kaul

Published Jan 1, 1979• 4 citations
Publisher

Abstract

The total cross section for excitation of ground state mercury atoms to the 63P1 state by 50 eV electrons was experimentally determined to be 0.434 ± 0.04 × 10−16 cm2. The apparatus used a pair of single-photon detectors to observe correlated optical photons in the 7 1S0 → 6 3P1 → 6 1S0 and 7 3S1 → 6 3P1 → 6 1S0 cascades. The product of the number of singles counts in the two detectors divided by the number of time-correlated cascade events was used along with angular distribution and correlation factors to determine N, the total number of atoms excited to the 6 3P1 state in the interaction region. The correct number N was arrived at in this way without making a separate determination of the overall photon detection efficiency. No standard lamp was needed for calibration nor was reference made to another standard cross section. The apparatus was self-calibrating. The absolute excitation cross section was determined from N and other parameters of the bombardment apparatus.

DOI
10.1364/josa.69.000150

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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.

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Sensitized Fluorescence in Sodium Induced in Collisions with Hg(63P1) Atoms

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Total cross sections for electrons scattered by 32 P3/2 sodium atoms

Bernardo Jaduszliwer, GF Shen, J.-L. Cai +1 more

An electron and photon atomic-recoil technique has been used to measure absolute total cross sections for electrons scattered by ${3}^{2}$${P}_{3/2}$ sodium atoms in the 6--25-eV energy range, with the use of a new, high-resolution crossed-beam apparatus. A single-mode tunable ring dye laser is used to selectively excite the F=3 hyperfine level. Excited-state populations are determined by using the atomic recoil in resonant photon absorption. At 6 eV there is very good agreement with a previous measurement [B. Jaduszliwer, R. Dang, P. Weiss, and B. Bederson, Phys. Rev. A 21, 808 (1980)].

Physical Review A•Feb 1, 1985•22 citations
The total cross section for excitation of ground state mercury atoms to the 63P1 state by 50 eV electrons was experimentally determined to be 0.434 ± 0.04 × 10−16 cm2. The apparatus used a pair of single-photon detectors to observe correlated optical photons in the 7 1S0 → 6 3P1 → 6 1S0 and 7 3S1 → 6 3P1 → 6 1S0 cascades. The product of the number of singles counts in the two detectors divided by the number of time-correlated cascade events was used along with angular distribution and correlation factors to determine N, the total number of atoms excited to the 6 3P1 state in the interaction region. The correct number N was arrived at in this way without making a separate determination of the overall photon detection efficiency. No standard lamp was needed for calibration nor was reference made to another standard cross section. The apparatus was self-calibrating. The absolute excitation cross section was determined from N and other parameters of the bombardment apparatus.
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.
Inclusion of collisional destruction mechanisms as sink terms in the theory of imprisonment of resonance radiation appears to have been neglected in the case of the 2537-Å mercury line. In this paper, the Holstein photon transport equation is employed to determine the effect of destructive or self-quenching collisions between resonance state and ground state atoms, processes in which the resonance state is converted to another excited state with the release of kinetic energy. These mechanisms seem to explain experimental work in which the decay constant of the 2537-Å mercury line reaches a minimum and then increases with density. Comparison of theory with experimental data yields a cross section between 3.0 and 10.0 × 10−18 for the conversion of Hg(3P1) to metastable Hg(3P0) by two-body collisions with Hg(1S0). The sharp increase at high density of the decay constant of the 2537-Å mercury line has not been predicted by previous theories but is a general consequence of the inclusion of collisional destruction mechanisms.
A nitrogen-seeded supersonic nozzle-beam source of metastable mercury, Hg(6 3P0),isdescribed.Ground-state(6 1S0)mercuryisexcited with 2537 Å resonance radiation to the 6 3P1 state, which is then converted via intramultiplet quenching to the 6 3P0 state collision with nitrogen (the carrier gas). The mercury beam is accelerated by the N2 seeding gas to a speed of 8×104 cm sec−1. Thus, the present source provides a beam of a single metastable state, Hg(6 3P0), with 4.67 eV of electronic excitation and 0.67 eV of translational energy. The metastable beam has been characterized and the kinetics of the over-all photoexcitation and quenching process studied by a secondary electron (Auger) detector utilizing a potassium surface, and an electron-bombardment ionizer, mass-filter detector. Hg(6 3P0) beam intensities of 4×1012 atoms sr−1⋅sec−1 are obtained, based upon an (assumed) 5% efficiency for the Auger detector.
Collisional transfer of excitation from mercury to sodium was investigated using methods of sensitized fluorescence. A mixture of mercury and sodium vapors at low pressure was irradiated with Hg 2537 Å resonance radiation, producing a population of Hg(63P1) atoms whose inelastic collisions with ground-state sodium atoms resulted in a transfer of excitation energy to close-lying S, P, and D states in sodium. The subsequent decay of these states manifested itself in the emission of a sensitized fluorescent spectrum. Absolute intensity measurements on the components of the spectrum yielded 21 cross sections whose magnitudes range from 0.02 to 38.5 Å2 and which exhibit a pronounced resonance with ΔE, the energy defect between Hg (63P1) and the appropriate level in sodium.
We have measured the alignment of the photofragments produced by photodissociation of Hg–Ar van der Waals molecules using light around 253.7 nm. The molecules are produced in the X0+ ground state in a supersonic expansion. Tunable laser light close to the Hg 6 1S0–6 3P1 transition is then used to excite the molecule to the B1± state, in which it dissociates. The alignment of the resulting Hg(3P1) asymptotic atoms is probed by tuning a delayed second laser to the 435.8 nm Hg 6 3P1–7 3S1 atomic transition and monitoring the subsequent fluorescence on the 7 3S1–6 3P2 transition around 546.1 nm. These measurements have been made, we believe for the first time, as a function of dissociating energy from very close to threshold to higher energies. The alignment shows a significant rise with increasing photon energy in line with a semiclassical picture of orbital locking at lower energies and rapid decoupling at higher energies. The results exhibit good agreement with the results of a fully quantum mechanical theory of the system.
An electron and photon atomic-recoil technique has been used to measure absolute total cross sections for electrons scattered by 32{3}^{2}32P3/2{P}_{3/2}P3/2​ sodium atoms in the 6--25-eV energy range, with the use of a new, high-resolution crossed-beam apparatus. A single-mode tunable ring dye laser is used to selectively excite the F=3 hyperfine level. Excited-state populations are determined by using the atomic recoil in resonant photon absorption. At 6 eV there is very good agreement with a previous measurement [B. Jaduszliwer, R. Dang, P. Weiss, and B. Bederson, Phys. Rev. A 21, 808 (1980)].