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Physical Review A

Isotropic collision-induced scattering from high-temperature gaseous mercury

Marco Sampoli, F. Hensel, F. Barocchi

Published Jun 1, 1996• 12 citations
Publisher

Abstract

We have measured the isotropic collision-induced light-scattering spectrum of a metal vapor, i.e., mercury vapor at temperature T=973 K and densities around 0.113 atom/${\mathrm{nm}}^{3}$, by means of an apparatus which allows us to perform comparisons between polarized and depolarized Raman spectra in high-temperature high-pressure gases and metal vapors. We have then derived an empirical model for the collision-induced polarizability trace of mercury diatom. Similarly to the anisotropy, the obtained trace behaves rather differently from the noble-gas counterpart, showing strong contributions from the electron correlations in the overlap region. \textcopyright{} 1996 The American Physical Society.

DOI
10.1103/physreva.53.4594

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Cross sections for relaxation of circular and linear polarization of $6^{2}P_{\frac{3}{2}}$ cesium atoms, induced in collisions with ground-state He, Ne, Ar, and Xe, have been determined by Zeeman scanning techniques. A fluorescence cell containing low-pressure cesium vapor together with a buffer gas was irradiated with circularly or linearly polarized 8521-\AA{} Cs resonance radiation, producing excited and polarized Cs atoms which became depolarized in subsequent collisions with the buffer-gas atoms. The resulting depolarization of the cesium resonance fluorescence was monitored in relation to buffer-gas pressure (0-10 Torr) and to the strength of the ambient magnetic field (0-10 kG). At low fields at which the nuclear spin $\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}}$ is coupled to the electronic angular momentum $\stackrel{\ensuremath{\rightarrow}}{\mathrm{J}}$, the measurements yielded depolarization cross sections $Q(\mathrm{circ}.)$ and $Q(\mathrm{lin}.)$, which agree within experimental error with theoretical values calculated for spin-coupled conditions. At kilogauss fields with $\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}}$ and $\stackrel{\ensuremath{\rightarrow}}{\mathrm{J}}$ decoupled, the experiments produced cross sections for disorientation and disalignment, which are also in satisfactory agreement with the appropriate theoretical predictions. The results indicate that the nuclear spin has a more pronounced effect on the collisional relaxation of the atomic dipole than of the quadrupole.

Physical Review A•Dec 1, 1976•13 citations
We have measured the isotropic collision-induced light-scattering spectrum of a metal vapor, i.e., mercury vapor at temperature T=973 K and densities around 0.113 atom/nm3{\mathrm{nm}}^{3}nm3, by means of an apparatus which allows us to perform comparisons between polarized and depolarized Raman spectra in high-temperature high-pressure gases and metal vapors. We have then derived an empirical model for the collision-induced polarizability trace of mercury diatom. Similarly to the anisotropy, the obtained trace behaves rather differently from the noble-gas counterpart, showing strong contributions from the electron correlations in the overlap region. \textcopyright{} 1996 The American Physical Society.
Isotropic depolarizing collisions are studied using a stimulated photon echo with a specific polarization of the excitation radiation pulses in a mixture of ytterbium with krypton for the J = 1 ⇄ J = 0 transition of 174Yb. The difference between the relaxation rates of orientation and alignment γ (2) − γ (1) of the 3 P 1(6s6p) 174Yb level is measured as a function of the krypton pressure. The collision photon echo at the J = 1 ⇄ J = 0 transition induced by the anisotropic relaxation is studied for the Yb + Xe mixture. The power of the collision echo increases from zero with the addition of a buffer gas to ytterbium, reaches an optimal level, and decreases with an increase in the buffer gas pressure. The polarization of this collision-induced echo differs from the polarization of the conventional echo. The experimental results are in qualitative agreement with theoretical predictions.
A photon echo induced exclusively by collisions of ytterbium atoms with buffer gas atoms has been observed at a 0 ⟷ 1-type1 S 0(6s 2)-3 P 1(6s6p) 174Yb transition. The polarization properties of a collision echo and the buffer gas density dependence of its intensity agree with theoretical predictions of a model of depolarizing collisions that takes into account the dependence of a relaxation matrix on the velocity of active particles. Thus, direct experimental evidence of the relaxation anisotropy due to depolarizing collisions has been obtained.
We have experimentally investigated the density behavior of the depolarized-interaction-induced light-scattering line shape of compressed gaseous argon at T=298 K and up to pressure p=262 MPa, i.e., to densities n=19.7 atoms/nm3{\mathrm{nm}}^{3}nm3. We have been able to measure the spectral behavior down to the frequency \ensuremath{\nu}\ensuremath{\approxeq}15 GHz. These low-frequency measurements have permitted the study in detail of the effect of the intensity cancellation which, in the line shape, manifests itself by means of a strong density-dependent rounding of the spectra below \ensuremath{\approxeq}900 GHz.
The cross sections for disorientation of 32P1/2 sodium atoms, induced in collisions with noble gas atoms, have been determined by following the depolarization of Na–D1 resonance fluorescence in relation to noble gas pressure. Sodium vapor at low density, mixed with a noble gas in a fluorescence cell, was irradiated with circularly polarized D1 resonance radiation and the resulting D1 resonance fluorescence, observed in an approximately backward direction, was analyzed with respect to circular polarization. The variation of the degree of polarization with gas pressure was interpreted on the basis of a 'J randomization' model for the collisions, and yielded the following disorientation cross sections which are appropriately corrected for effects due to nuclear spin. Na–He: 28.1 ± 4.0 Å2; Na–Ne: 27.8 ± 4.0 Å2; Na–Ar: 57.0 ± 8.0 Å2; Na–Kr: 78.0 ± 10 Å2; Na–Xe: 87.0 ± 13 Å2.
Depolarization and quenching of mercury resonance radiation are phenomena of quite different type. Depolarization is produced by two effects. With gases which quench by effecting the transition $^{3}P_{1}\ensuremath{\rightarrow}^{3}P_{0}$ upon collision with Hg\ensuremath{'} atoms, there exists a pronounced reverse transition $^{3}P_{0}\ensuremath{\rightarrow}^{3}P_{1}$ produced by collision with high speed molecules. Atoms which radiate without any collision emit polarized light under the conditions of the experiment. Those which become 3P1^{3}P_{1}3P1​ atoms after having existed as 3P0^{3}P_{0}3P0​ atoms have experienced a large number of collisions and have lost their orientation relative to the incident electric vector; accordingly they emit radiation polarized in random directions. The second depolarizing influence arises in collisions at distances exceeding the ordinary kinetic theory collision such as is described above, at which the distance is too great for a collision of the first or second type, but still small enough for the field of the gas atom to exert a perturbing influence on the orientation of the Hg\ensuremath{'} atom. Depolarization by H2{\mathrm{H}}_{2}H2​ is an excellent example of the second influence while the first effect is sufficient to interpret the experimental data with the rare gases, the atomic fields of which decrease with a high power of the radial distance.
Cross sections for relaxation of circular and linear polarization of 62P326^{2}P_{\frac{3}{2}}62P23​​ cesium atoms, induced in collisions with ground-state He, Ne, Ar, and Xe, have been determined by Zeeman scanning techniques. A fluorescence cell containing low-pressure cesium vapor together with a buffer gas was irradiated with circularly or linearly polarized 8521-\AA{} Cs resonance radiation, producing excited and polarized Cs atoms which became depolarized in subsequent collisions with the buffer-gas atoms. The resulting depolarization of the cesium resonance fluorescence was monitored in relation to buffer-gas pressure (0-10 Torr) and to the strength of the ambient magnetic field (0-10 kG). At low fields at which the nuclear spin $\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}}$ is coupled to the electronic angular momentum $\stackrel{\ensuremath{\rightarrow}}{\mathrm{J}}$, the measurements yielded depolarization cross sections Q(circ.)Q(\mathrm{circ}.)Q(circ.) and Q(lin.)Q(\mathrm{lin}.)Q(lin.), which agree within experimental error with theoretical values calculated for spin-coupled conditions. At kilogauss fields with $\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}}$ and $\stackrel{\ensuremath{\rightarrow}}{\mathrm{J}}$ decoupled, the experiments produced cross sections for disorientation and disalignment, which are also in satisfactory agreement with the appropriate theoretical predictions. The results indicate that the nuclear spin has a more pronounced effect on the collisional relaxation of the atomic dipole than of the quadrupole.