Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physical Review A

Electronic spin relaxation of the 4S122 state of K induced by K-He and K-Ne collisions

F. A. Franz, C. H. Volk

Published Jul 1, 1982• 21 citations
Publisher

Abstract

Electronic and nuclear spin relaxation of optically pumped K atoms has been measured in the presence of He and Ne gases. The nuclear-spin-independent cross sections for the destruction of electronic spin polarization in the $4^{2}S_{\frac{1}{2}}$ ground state of K are $\ensuremath{\sigma}[\ensuremath{\gamma}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{N}})](\mathrm{K}\ensuremath{-}\mathrm{He})=8.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}25}$ ${\mathrm{cm}}^{2}$ and $\ensuremath{\sigma}[\ensuremath{\gamma}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{N}})](\mathrm{K}\ensuremath{-}\mathrm{Ne})=141\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}25}$ ${\mathrm{cm}}^{2}$. The diffusion coefficients of K in He and Ne, corrected to 273 K, are ${D}_{0}(\mathrm{K}\ensuremath{-}\mathrm{He})=0.35$ ${\mathrm{cm}}^{2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ and ${D}_{0}(\mathrm{K}\ensuremath{-}\mathrm{Ne})=0.19$ ${\mathrm{cm}}^{2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$. All measurements have an estimated uncertainty of \ifmmode\pm\else\textpm\fi{}10%. The relaxation of K is shown to be strongly affected by an anomalous process which is attributed to the modification of the K hyperfine interaction induced by the formation of K-He and K-Ne van der Waals complexes.

DOI
10.1103/physreva.26.85

Related papers

Spin relaxation of of rubidium atoms induced by collisional modification of the Rb hyperfine interaction

F. A. Franz, A. Sieradzan

Spin relaxation of Rb atoms induced by collisional modification of the hyperfine interaction has been measured for $^{85}\mathrm{Rb}$ and $^{87}\mathrm{Rb}$ in He, Ne, and Ar buffer gases at high magnetic field. The relaxation rates at 40 kG are 0.028 ${\mathrm{sec}}^{\ensuremath{-}1}$ ${\mathrm{Torr}}^{\ensuremath{-}1}$ for $^{85}\mathrm{Rb}$ in He, 0.029 ${\mathrm{sec}}^{\ensuremath{-}1}$ ${\mathrm{Torr}}^{\ensuremath{-}1}$ for $^{85}\mathrm{Rb}$ in Ne, and 0.041 ${\mathrm{sec}}^{\ensuremath{-}1}$ ${\mathrm{Torr}}^{\ensuremath{-}1}$ for $^{85}\mathrm{Rb}$ in Ar. The corresponding relaxation rates for $^{87}\mathrm{Rb}$ are approximately 4.9 times larger, in accord with theory. Cross sections for the binary $\ensuremath{\delta}a(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}})$ collisional interaction are estimated to be $\ensuremath{\sigma}(\ensuremath{\delta}a(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}}))(\mathrm{Rb}\ensuremath{-}\mathrm{He})=2.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{2}$ and $\ensuremath{\sigma}(\ensuremath{\delta}a(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}}))(\mathrm{Rb}\ensuremath{-}\mathrm{Ne})=1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{2}$. Anomalous relaxation, ${R}^{*}$, is present in the same degree at 40 kG as at low magnetic field, lending strong support to earlier attributions of ${R}^{*}$ to the $\ensuremath{\delta}a(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}})$ interaction in Rb-atom-noble-gas-atom van der Waals molecules.

Physical Review A•Jun 1, 1981•10 citations

Spin relaxation in Rb-He and Rb-Ne via modification of the Rb hyperfine interaction in Van der Waals molecules

F. A. Franz, C. H. Volk

Anomalous modes of electronic-spin relaxation of optically pumped Rb atoms observed in He and Ne buffer gases may result from the modification of the Rb hyperfine interaction, induced by the formation of Rb-He and Rb-Ne Van der Waals molecules. Isolation of anomalous effects also resolves disagreements in cross sections previously reported for the spin relaxation of Cs in Ne.

Physical Review A•Aug 1, 1978•12 citations

Cross Sections for Excited-State Mixing in Cesium-Noble-Gas Collisions from D2 Optical Pumping

Jochen Fricke, J. Haas, E. Lüscher +1 more

Cross sections for random collisional reorientation of J within the sublevels of the $6^{2}P_{\frac{3}{2}}$ excited state of cesium have been measured using the ${D}_{2}$ optical-pumping technique. The measured cross sections ${{\ensuremath{\sigma}}_{M}}^{2}$ are: Cs-He (3.2\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$, Cs-Ne (2.9\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$, Cs-Ar (6.0\ifmmode\pm\else\textpm\fi{}1.2)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$, Cs-Kr (9.2\ifmmode\pm\else\textpm\fi{}1.9)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$, Cs-Xe (11.3\ifmmode\pm\else\textpm\fi{}2.3)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$. Simplified equations for ${\mathrm{D}}_{1}$ and ${\mathrm{D}}_{2}$ pumping with zero, partial, and complete excited-state mixing are derived for a hypothetical alkali atom with zero nuclear spin. The calculations are extended to cesium atoms with nuclear spin $\frac{7}{2}$ pumped by ${\ensuremath{\sigma}}^{+}$ ${\mathrm{D}}_{2}$ radiation. The equilibrium value ${〈{S}_{z}〉}_{0}$ and the time dependence $〈{S}_{z}(t)〉$ of the electronic spin polarization are computed for various degrees of excited-state mixing. $〈{S}_{z}(t)〉$ is found to be nearly single-exponential in the zero- and the complete-mixing cases, but shows a distinct double-exponential behavior in the intermediate region. ${〈{S}_{z}〉}_{0}$ is shown to be dependent on the degree of mixing, and to change sign as the degree of mixing increases. Measurements were performed with a new transmission technique by passing a separate ${\ensuremath{\sigma}}^{+}$-polarized ${\mathrm{D}}_{2}$ pumping beam and an alternately ${\ensuremath{\sigma}}^{+}$- and ${\ensuremath{\sigma}}^{\ensuremath{-}}$-polarized ${\mathrm{D}}_{1}$ testing beam through the cesium absorption cell. The cross sections for collisionally induced mixing were evaluated by measuring the buffer pressure at which ${〈{S}_{z}〉}_{0}$ passed through zero.

Physical Review•Nov 5, 1967•34 citations

Depolarization of 6P322 cesium atoms, induced in collisions with noble gases

J. Guiry, L. Krause

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

Optical Pumping and Collisional Relaxation in the P122 Ground State of Thallium

H. M. Gibbs, G. G. Churchill, T. Marshall +2 more

The $^{2}P_{\frac{1}{2}}$ ground state of thallium has been optically pumped in the presence of various buffer gases. The measured cross sections for the destruction of the electron polarization are small (${10}^{\ensuremath{-}19}$ to ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$), verifying the selection rule ${M}_{J}\ensuremath{\nrightarrow}\ensuremath{-}{M}_{J}$ for the adiabatic contributions and demonstrating the strong dependence of the nonadiabatic contributions upon the multiplet energy separation.

Physical Review Letters•Aug 3, 1970•25 citations

Spin relaxation of rubidium atoms in sudden and quasimolecular collisions with light-noble-gas atoms

F. A. Franz, C. H. Volk

Spin relaxation of optically pumped ${\mathrm{Rb}}^{85}$ and ${\mathrm{Rb}}^{87}$ atoms colliding with light-noble-gas atoms is shown to be strongly influenced by an anomalous relaxation process which we attribute to the formation and destruction of bound and quasibound Van der Waals molecules. The anomalous relaxation rate has been measured and analyzed in Ne, complementing an earlier study in He. Relative rates of formation of complexes in two- and three-body collisions have been determined. The correlation time for the quasimolecular interaction in Rb-Ne has been found to be 6.7 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}10}$ ${p}^{\ensuremath{-}1}$ sec, where $p$ is the Ne pressure in Torr. Nuclear-spin-independent cross sections for the relaxation of $〈{S}_{z}〉$ in sudden binary collisions of Rb atoms with noble-gas atoms have been measured to be (units of ${10}^{\ensuremath{-}24}$ ${\mathrm{cm}}^{2}$: $\ensuremath{\sigma}(\mathrm{Rb}\ensuremath{-}\mathrm{He})=3.1$ $\ensuremath{\sigma}(\mathrm{Rb}\ensuremath{-}\mathrm{Ne})=19$ $\ensuremath{\sigma}(\mathrm{Rb}\ensuremath{-}\mathrm{Ar})=630$ $\ensuremath{\sigma}(\mathrm{Rb}\ensuremath{-}{\mathrm{N}}_{2})=83$. Relaxation in sudden binary collisions is shown to follow the theoretically expected nuclear spin dynamics: two relaxation rates in the ratios 8:1 for ${\mathrm{Rb}}^{87}$ and 18:1 for ${\mathrm{Rb}}^{85}$ have been measured. Diffusion coefficients of Rb in the various buffer gases have been measured to be (units of ${\mathrm{cm}}^{2}$/ sec, at 305\ifmmode^\circ\else\textdegree\fi{}K): ${D}_{0}(\mathrm{Rb}\ensuremath{-}\mathrm{He})=0.42$, ${D}_{0}(\mathrm{Rb}\ensuremath{-}\mathrm{Ne})=0.235$, ${D}_{0}(\mathrm{Rb}\ensuremath{-}\mathrm{Ar})=0.16$, ${D}_{0}(\mathrm{Rb}\ensuremath{-}{\mathrm{N}}_{2})=0.16$. Nuclear-spin-independent cross sections for the relaxation of $〈{J}_{z}〉$ in the $5^{2}P_{\frac{1}{2}}$ state of Rb have been measured to be 3.4 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ for Rb-He, and 5.9 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ for Rb-Ne. Anomalies, disagreements, and puzzles occurring in earlier measurements of ground-state relaxation in Rb are shown to be largely resolved when considered in the light of the new results.

Physical Review A•Nov 1, 1976•55 citations
Electronic and nuclear spin relaxation of optically pumped K atoms has been measured in the presence of He and Ne gases. The nuclear-spin-independent cross sections for the destruction of electronic spin polarization in the 42S124^{2}S_{\frac{1}{2}}42S21​​ ground state of K are \ensuremathσ[\ensuremathγ(S\ensuremath→\ifmmode⋅\else\textperiodcentered\fiN\ensuremath→)](K\ensuremath−He)=8.0\ifmmode×\else\texttimes\fi10\ensuremath−25\ensuremath{\sigma}[\ensuremath{\gamma}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{N}})](\mathrm{K}\ensuremath{-}\mathrm{He})=8.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}25}\ensuremathσ[\ensuremathγ(S\ensuremath→​\ifmmode⋅\else\textperiodcentered\fiN\ensuremath→​)](K\ensuremath−He)=8.0\ifmmode×\else\texttimes\fi10\ensuremath−25 cm2{\mathrm{cm}}^{2}cm2 and \ensuremathσ[\ensuremathγ(S\ensuremath→\ifmmode⋅\else\textperiodcentered\fiN\ensuremath→)](K\ensuremath−Ne)=141\ifmmode×\else\texttimes\fi10\ensuremath−25\ensuremath{\sigma}[\ensuremath{\gamma}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{N}})](\mathrm{K}\ensuremath{-}\mathrm{Ne})=141\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}25}\ensuremathσ[\ensuremathγ(S\ensuremath→​\ifmmode⋅\else\textperiodcentered\fiN\ensuremath→​)](K\ensuremath−Ne)=141\ifmmode×\else\texttimes\fi10\ensuremath−25 cm2{\mathrm{cm}}^{2}cm2. The diffusion coefficients of K in He and Ne, corrected to 273 K, are D0(K\ensuremath−He)=0.35{D}_{0}(\mathrm{K}\ensuremath{-}\mathrm{He})=0.35D0​(K\ensuremath−He)=0.35 cm2{\mathrm{cm}}^{2}cm2 sec\ensuremath−1{\mathrm{sec}}^{\ensuremath{-}1}sec\ensuremath−1 and D0(K\ensuremath−Ne)=0.19{D}_{0}(\mathrm{K}\ensuremath{-}\mathrm{Ne})=0.19D0​(K\ensuremath−Ne)=0.19 cm2{\mathrm{cm}}^{2}cm2 sec\ensuremath−1{\mathrm{sec}}^{\ensuremath{-}1}sec\ensuremath−1. All measurements have an estimated uncertainty of \ifmmode\pm\else\textpm\fi{}10%. The relaxation of K is shown to be strongly affected by an anomalous process which is attributed to the modification of the K hyperfine interaction induced by the formation of K-He and K-Ne van der Waals complexes.
Spin relaxation of Rb atoms induced by collisional modification of the hyperfine interaction has been measured for 85Rb^{85}\mathrm{Rb}85Rb and 87Rb^{87}\mathrm{Rb}87Rb in He, Ne, and Ar buffer gases at high magnetic field. The relaxation rates at 40 kG are 0.028 ${\mathrm{sec}}^{\ensuremath{-}1}$ ${\mathrm{Torr}}^{\ensuremath{-}1}$ for 85Rb^{85}\mathrm{Rb}85Rb in He, 0.029 ${\mathrm{sec}}^{\ensuremath{-}1}$ ${\mathrm{Torr}}^{\ensuremath{-}1}$ for 85Rb^{85}\mathrm{Rb}85Rb in Ne, and 0.041 ${\mathrm{sec}}^{\ensuremath{-}1}$ ${\mathrm{Torr}}^{\ensuremath{-}1}$ for 85Rb^{85}\mathrm{Rb}85Rb in Ar. The corresponding relaxation rates for 87Rb^{87}\mathrm{Rb}87Rb are approximately 4.9 times larger, in accord with theory. Cross sections for the binary $\ensuremath{\delta}a(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}})$ collisional interaction are estimated to be $\ensuremath{\sigma}(\ensuremath{\delta}a(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}}))(\mathrm{Rb}\ensuremath{-}\mathrm{He})=2.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ cm2{\mathrm{cm}}^{2}cm2 and $\ensuremath{\sigma}(\ensuremath{\delta}a(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}}))(\mathrm{Rb}\ensuremath{-}\mathrm{Ne})=1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ cm2{\mathrm{cm}}^{2}cm2. Anomalous relaxation, R∗{R}^{*}R∗, is present in the same degree at 40 kG as at low magnetic field, lending strong support to earlier attributions of R∗{R}^{*}R∗ to the $\ensuremath{\delta}a(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}})$ interaction in Rb-atom-noble-gas-atom van der Waals molecules.
Cross sections for random collisional reorientation of J within the sublevels of the 62P326^{2}P_{\frac{3}{2}}62P23​​ excited state of cesium have been measured using the D2{D}_{2}D2​ optical-pumping technique. The measured cross sections ${{\ensuremath{\sigma}}_{M}}^{2}$ are: Cs-He (3.2\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}15}$ cm2{\mathrm{cm}}^{2}cm2, Cs-Ne (2.9\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}15}$ cm2{\mathrm{cm}}^{2}cm2, Cs-Ar (6.0\ifmmode\pm\else\textpm\fi{}1.2)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}15}$ cm2{\mathrm{cm}}^{2}cm2, Cs-Kr (9.2\ifmmode\pm\else\textpm\fi{}1.9)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}15}$ cm2{\mathrm{cm}}^{2}cm2, Cs-Xe (11.3\ifmmode\pm\else\textpm\fi{}2.3)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}15}$ cm2{\mathrm{cm}}^{2}cm2. Simplified equations for D1{\mathrm{D}}_{1}D1​ and D2{\mathrm{D}}_{2}D2​ pumping with zero, partial, and complete excited-state mixing are derived for a hypothetical alkali atom with zero nuclear spin. The calculations are extended to cesium atoms with nuclear spin 72\frac{7}{2}27​ pumped by ${\ensuremath{\sigma}}^{+}$ D2{\mathrm{D}}_{2}D2​ radiation. The equilibrium value 〈Sz〉0{〈{S}_{z}〉}_{0}〈Sz​〉0​ and the time dependence 〈Sz(t)〉〈{S}_{z}(t)〉〈Sz​(t)〉 of the electronic spin polarization are computed for various degrees of excited-state mixing. 〈Sz(t)〉〈{S}_{z}(t)〉〈Sz​(t)〉 is found to be nearly single-exponential in the zero- and the complete-mixing cases, but shows a distinct double-exponential behavior in the intermediate region. 〈Sz〉0{〈{S}_{z}〉}_{0}〈Sz​〉0​ is shown to be dependent on the degree of mixing, and to change sign as the degree of mixing increases. Measurements were performed with a new transmission technique by passing a separate ${\ensuremath{\sigma}}^{+}$-polarized D2{\mathrm{D}}_{2}D2​ pumping beam and an alternately ${\ensuremath{\sigma}}^{+}$- and ${\ensuremath{\sigma}}^{\ensuremath{-}}$-polarized D1{\mathrm{D}}_{1}D1​ testing beam through the cesium absorption cell. The cross sections for collisionally induced mixing were evaluated by measuring the buffer pressure at which 〈Sz〉0{〈{S}_{z}〉}_{0}〈Sz​〉0​ passed through zero.
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.
The 2P12^{2}P_{\frac{1}{2}}2P21​​ ground state of thallium has been optically pumped in the presence of various buffer gases. The measured cross sections for the destruction of the electron polarization are small (${10}^{\ensuremath{-}19}$ to ${10}^{\ensuremath{-}17}$ cm2{\mathrm{cm}}^{2}cm2), verifying the selection rule ${M}_{J}\ensuremath{\nrightarrow}\ensuremath{-}{M}_{J}$ for the adiabatic contributions and demonstrating the strong dependence of the nonadiabatic contributions upon the multiplet energy separation.
Spin relaxation of optically pumped Rb85{\mathrm{Rb}}^{85}Rb85 and Rb87{\mathrm{Rb}}^{87}Rb87 atoms colliding with light-noble-gas atoms is shown to be strongly influenced by an anomalous relaxation process which we attribute to the formation and destruction of bound and quasibound Van der Waals molecules. The anomalous relaxation rate has been measured and analyzed in Ne, complementing an earlier study in He. Relative rates of formation of complexes in two- and three-body collisions have been determined. The correlation time for the quasimolecular interaction in Rb-Ne has been found to be 6.7 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}10}$ ${p}^{\ensuremath{-}1}$ sec, where ppp is the Ne pressure in Torr. Nuclear-spin-independent cross sections for the relaxation of 〈Sz〉〈{S}_{z}〉〈Sz​〉 in sudden binary collisions of Rb atoms with noble-gas atoms have been measured to be (units of ${10}^{\ensuremath{-}24}$ cm2{\mathrm{cm}}^{2}cm2: $\ensuremath{\sigma}(\mathrm{Rb}\ensuremath{-}\mathrm{He})=3.1$ $\ensuremath{\sigma}(\mathrm{Rb}\ensuremath{-}\mathrm{Ne})=19$ $\ensuremath{\sigma}(\mathrm{Rb}\ensuremath{-}\mathrm{Ar})=630$ $\ensuremath{\sigma}(\mathrm{Rb}\ensuremath{-}{\mathrm{N}}_{2})=83$. Relaxation in sudden binary collisions is shown to follow the theoretically expected nuclear spin dynamics: two relaxation rates in the ratios 8:1 for Rb87{\mathrm{Rb}}^{87}Rb87 and 18:1 for Rb85{\mathrm{Rb}}^{85}Rb85 have been measured. Diffusion coefficients of Rb in the various buffer gases have been measured to be (units of cm2{\mathrm{cm}}^{2}cm2/ sec, at 305\ifmmode^\circ\else\textdegree\fi{}K): ${D}_{0}(\mathrm{Rb}\ensuremath{-}\mathrm{He})=0.42$, ${D}_{0}(\mathrm{Rb}\ensuremath{-}\mathrm{Ne})=0.235$, ${D}_{0}(\mathrm{Rb}\ensuremath{-}\mathrm{Ar})=0.16$, ${D}_{0}(\mathrm{Rb}\ensuremath{-}{\mathrm{N}}_{2})=0.16$. Nuclear-spin-independent cross sections for the relaxation of 〈Jz〉〈{J}_{z}〉〈Jz​〉 in the 52P125^{2}P_{\frac{1}{2}}52P21​​ state of Rb have been measured to be 3.4 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ cm2{\mathrm{cm}}^{2}cm2 for Rb-He, and 5.9 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ cm2{\mathrm{cm}}^{2}cm2 for Rb-Ne. Anomalies, disagreements, and puzzles occurring in earlier measurements of ground-state relaxation in Rb are shown to be largely resolved when considered in the light of the new results.