Measurements of the collisional relaxation of the potassium resonance levels are reported. Effects due to the presence of nuclear spin are allowed for in the case of 2 P 1/2 and found to be negligible in the case of 2 P 3/2 . Reasonable overall agreement is found with calculated cross sections based on the Pascale and Vandeplanque potentials (1974). The natural lifetimes of the resonance levels are found to be tau ( 2 P 1/2 )=25.0+or-0.3 ns and tau ( 2 P 3/2 )=26.3+or-1.0 ns, and the sum of the resonance values is in good agreement with recent SCF calculations.
Measurements of the collisional relaxation of the potassium resonance levels are reported. Effects due to the presence of nuclear spin are allowed for in the case of 2 P 1/2 and found to be negligible in the case of 2 P 3/2 . Reasonable overall agreement is found with calculated cross sections based on the Pascale and Vandeplanque potentials (1974). The natural lifetimes of the resonance levels are found to be tau ( 2 P 1/2 )=25.0+or-0.3 ns and tau ( 2 P 3/2 )=26.3+or-1.0 ns, and the sum of the resonance values is in good agreement with recent SCF calculations.
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.
Collisional excitation transfer and relaxation of K 5sp2P 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 5sp2Psb1over2 or the 5sp2Psb3over2 state in zero magnetic field and to the 5sp2Psb1over2−1over2 or the 5sp2Psb3over2−3over2 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.
Cross sections for relaxation of circular and linear polarization of 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.) and 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.
The cross sections for disorientation of 42P1/2 potassium atoms, induced in collisions with noble gas atoms, have been determined in zero magnetic field by studying the depolarization of K(7699 Å) resonance fluorescence in relation to noble gas pressures. Potassium vapor at low density, mixed with a noble gas in a fluorescence vessel, was irradiated with circularly polarized 7699 Å potassium resonance radiation and the resulting 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 the effect of nuclear spin: K–He, 24 ± 4 Å2; K–Ne, 21 ± 3 Å2; K–Ar, 37 ± 5 Å2; K–Kr, 51 ± 7 Å2; K–Xe, 69 ± 9 Å2. The cross sections are significantly smaller than values obtained previously in kilogauss fields.
mJ mixing in 42P21 and 42P23 potassium atoms as well as atomic multipole relaxation induced in K-K and K-Ar collisions were investigated by methods of atomic fluorescence spectroscopy. K vapor, pure or mixed with Ar, was placed in a kG magnetic field and irradiated with a single Zeeman component of 7665- or 7699-\AA{} resonance radiation, causing the selective excitation of the $^{2}P_{\frac{1}{2},\ensuremath{-}\frac{1}{2}}$ or $^{2}P_{\frac{3}{2},\ensuremath{-}\frac{3}{2}}$ substate. Collisions of the excited atoms with ground-state K or Ar atoms caused mJ mixing which was monitored by analysis of the resulting fluorescent spectrum with a scanning Fabry-Perot interferometer. Intensity measurements on the fluorescent Zeeman components in relation to ground-state atomic densities yielded the following multipole relaxation cross sections ${\ensuremath{\Lambda}}_{J}^{(L)}$: K-K (${10}^{\ensuremath{-}12}$ cm2): ${\ensuremath{\Lambda}}_{\frac{1}{2}}^{(1)}=5.7\ifmmode\pm\else\textpm\fi{}0.9$, ${\ensuremath{\Lambda}}_{\frac{3}{2}}^{(1)}=8.1\ifmmode\pm\else\textpm\fi{}1.4$, ${\ensuremath{\Lambda}}_{\frac{3}{2}}^{(2)}=11.4\ifmmode\pm\else\textpm\fi{}2.0$, ${\ensuremath{\Lambda}}_{\frac{3}{2}}^{(3)}=9.8\ifmmode\pm\else\textpm\fi{}1.5$; K-Ar (${10}^{\ensuremath{-}16}$ cm2): ${\ensuremath{\Lambda}}_{\frac{1}{2}}^{(1)}=65\ifmmode\pm\else\textpm\fi{}10$, ${\ensuremath{\Lambda}}_{\frac{3}{2}}^{(1)}=175\ifmmode\pm\else\textpm\fi{}25$, ${\ensuremath{\Lambda}}_{\frac{3}{2}}^{(2)}=230\ifmmode\pm\else\textpm\fi{}35$, ${\ensuremath{\Lambda}}_{\frac{3}{2}}^{(3)}=190\ifmmode\pm\else\textpm\fi{}30$. The ${Q}_{J}(m\ensuremath{\leftrightarrow}{m}^{\ensuremath{'}})$ cross sections for mJ mixing were derived from the ${\ensuremath{\Lambda}}_{J}^{(L)}$ as well as the cross sections for multipole decay ${\ensuremath{\sigma}}_{J}^{(L)}={\ensuremath{\Lambda}}_{J}^{(L)}+{\ensuremath{\sigma}}_{J}^{(0)}$. The experimental results are in good agreement with theoretical calculations.