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

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

F. A. Franz, A. Sieradzan

Published Jun 1, 1981• 10 citations
Publisher

Abstract

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.

DOI
10.1103/physreva.23.2841

Related papers

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

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

Rubidium Spin Relaxation in the Rare Gases Under Ultraclean Conditions

F. A. Franz

The spin relaxation of optically pumped rubidium vapor induced by rubidium-rare-gas atomic collisions has been investigated in an ultraclean environment. The experiment was performed under conditions such that the partial pressure of nonrare-gas impurities was less than 1\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ Torr, and that the time between Rb-Rb spin exchange collisions was short compared to the spin relaxation time. The cross sections (in ${\mathrm{cm}}^{2}$) for disorientation of rubidium were found to be: He, 3.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}25}$; Ne, 3.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}24}$; Ar, 1.1\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}22}$; Kr, 7.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}21}$; Xe, 1.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}19}$. The fact that these cross sections are considerably smaller than previously reported values is attributed primarily to the low degree of impurity contamination in the present work. When compared with already existing values for cesium and sodium, the disorientation cross sections of these three alkali metals are seen to have a remarkably similar dependence on buffer-gas atomic number. The new experimental values are also compared with recent theoretical calculations.

Physical Review•Aug 2, 1965•33 citations

Hyperfine Relaxation of Optically Pumped Rb87 Atoms in Buffer Gases

Maurice Arditi, T. R. Carver

The hyperfine relaxation of a population difference, produced by optical pumping, between the $F=1$ ${m}_{F}=0$ and $F=2$ ${m}_{F}=0$ energy levels of the ground state of ${\mathrm{Rb}}^{87}$, has been studied in cells containing neon, argon, helium, or krypton as a buffer gas. The relaxation times ${T}_{1}$ and ${T}_{2}$ have been measured as a function of the rubidium vapor pressure in the cell. The relaxation rate due to spin exchange in ${\mathrm{Rb}}^{87}$-${\mathrm{Rb}}^{87}$ collisions has been found equal to 65 ${\mathrm{sec}}^{\ensuremath{-}1}$ at 44\ifmmode^\circ\else\textdegree\fi{}C, and the diffusion coefficients of ${\mathrm{Rb}}^{87}$ atoms in He, Ne, and Ar evaluated as 0.6, 0.31, and 0.22 ${\mathrm{cm}}^{2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, respectively. The cross section for ${\mathrm{Rb}}^{87}$-Ne and ${\mathrm{Rb}}^{87}$-Ar collisions are found to be 1.6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}22}$ ${\mathrm{cm}}^{2}$ and 9\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}22}$ ${\mathrm{cm}}^{2}$. These values are in general agreement with values previously obtained by other methods. The extrapolated values of $\frac{1}{{T}_{2}}$ for zero vapor pressure of rubidium are 185, 237, and 318 ${\mathrm{sec}}^{\ensuremath{-}1}$ for Ne, He, or Ar, respectively. Relaxations by the pumping light or by the magnetic field inhomogeneities are also discussed.

Physical Review•Nov 2, 1964•38 citations

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

F. A. Franz, C. H. Volk

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.

Physical Review A•Jul 1, 1982•21 citations

Magnetic decoupling of Rb spin relaxation in H2 buffer gas

P. I. Borel, Christopher Erickson, D. K. Walter

We report studies of the magnetic decoupling of Rb spin relaxation in the presence of ${\mathrm{H}}_{2}$ buffer gas at high pressures $(>~1.5\mathrm{atm}).$ At low Rb number densities $(<~5\ifmmode\times\else\texttimes\fi{}{10}^{13}{\mathrm{cm}}^{\ensuremath{-}3}),$ we find that the observed magnetic-field dependence of the spin relaxation is almost solely due to binary collisions between Rb atoms and hydrogen molecules, and that it is very well described by three rates: the Rb-Rb spin-exchange rate, the S-damping rate, and the Carver rate associated with the hyperfine pressure-shift interaction in collisions of Rb with ${\mathrm{H}}_{2}$ molecules. At higher Rb densities, the contribution to the relaxation from Rb triplet dimers becomes significant.

Physical Review A•Dec 20, 2002•1 citation
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 sec\ensuremath−1{\mathrm{sec}}^{\ensuremath{-}1}sec\ensuremath−1 Torr\ensuremath−1{\mathrm{Torr}}^{\ensuremath{-}1}Torr\ensuremath−1 for 85Rb^{85}\mathrm{Rb}85Rb in He, 0.029 sec\ensuremath−1{\mathrm{sec}}^{\ensuremath{-}1}sec\ensuremath−1 Torr\ensuremath−1{\mathrm{Torr}}^{\ensuremath{-}1}Torr\ensuremath−1 for 85Rb^{85}\mathrm{Rb}85Rb in Ne, and 0.041 sec\ensuremath−1{\mathrm{sec}}^{\ensuremath{-}1}sec\ensuremath−1 Torr\ensuremath−1{\mathrm{Torr}}^{\ensuremath{-}1}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 \ensuremathδa(S\ensuremath→\ifmmode⋅\else\textperiodcentered\fiI\ensuremath→)\ensuremath{\delta}a(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}})\ensuremathδa(S\ensuremath→​\ifmmode⋅\else\textperiodcentered\fiI\ensuremath→​) collisional interaction are estimated to be \ensuremathσ(\ensuremathδa(S\ensuremath→\ifmmode⋅\else\textperiodcentered\fiI\ensuremath→))(Rb\ensuremath−He)=2.3\ifmmode×\else\texttimes\fi10\ensuremath−14\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}\ensuremathσ(\ensuremathδa(S\ensuremath→​\ifmmode⋅\else\textperiodcentered\fiI\ensuremath→​))(Rb\ensuremath−He)=2.3\ifmmode×\else\texttimes\fi10\ensuremath−14 cm2{\mathrm{cm}}^{2}cm2 and \ensuremathσ(\ensuremathδa(S\ensuremath→\ifmmode⋅\else\textperiodcentered\fiI\ensuremath→))(Rb\ensuremath−Ne)=1.4\ifmmode×\else\texttimes\fi10\ensuremath−14\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}\ensuremathσ(\ensuremathδa(S\ensuremath→​\ifmmode⋅\else\textperiodcentered\fiI\ensuremath→​))(Rb\ensuremath−Ne)=1.4\ifmmode×\else\texttimes\fi10\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 \ensuremathδa(S\ensuremath→\ifmmode⋅\else\textperiodcentered\fiI\ensuremath→)\ensuremath{\delta}a(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{I}})\ensuremathδa(S\ensuremath→​\ifmmode⋅\else\textperiodcentered\fiI\ensuremath→​) interaction in Rb-atom-noble-gas-atom van der Waals molecules.
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.
The spin relaxation of optically pumped rubidium vapor induced by rubidium-rare-gas atomic collisions has been investigated in an ultraclean environment. The experiment was performed under conditions such that the partial pressure of nonrare-gas impurities was less than 1\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ Torr, and that the time between Rb-Rb spin exchange collisions was short compared to the spin relaxation time. The cross sections (in cm2{\mathrm{cm}}^{2}cm2) for disorientation of rubidium were found to be: He, 3.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}25}$; Ne, 3.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}24}$; Ar, 1.1\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}22}$; Kr, 7.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}21}$; Xe, 1.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}19}$. The fact that these cross sections are considerably smaller than previously reported values is attributed primarily to the low degree of impurity contamination in the present work. When compared with already existing values for cesium and sodium, the disorientation cross sections of these three alkali metals are seen to have a remarkably similar dependence on buffer-gas atomic number. The new experimental values are also compared with recent theoretical calculations.
The hyperfine relaxation of a population difference, produced by optical pumping, between the F=1F=1F=1 mF=0{m}_{F}=0mF​=0 and F=2F=2F=2 mF=0{m}_{F}=0mF​=0 energy levels of the ground state of Rb87{\mathrm{Rb}}^{87}Rb87, has been studied in cells containing neon, argon, helium, or krypton as a buffer gas. The relaxation times T1{T}_{1}T1​ and T2{T}_{2}T2​ have been measured as a function of the rubidium vapor pressure in the cell. The relaxation rate due to spin exchange in Rb87{\mathrm{Rb}}^{87}Rb87-Rb87{\mathrm{Rb}}^{87}Rb87 collisions has been found equal to 65 ${\mathrm{sec}}^{\ensuremath{-}1}$ at 44\ifmmode^\circ\else\textdegree\fi{}C, and the diffusion coefficients of Rb87{\mathrm{Rb}}^{87}Rb87 atoms in He, Ne, and Ar evaluated as 0.6, 0.31, and 0.22 cm2{\mathrm{cm}}^{2}cm2 ${\mathrm{sec}}^{\ensuremath{-}1}$, respectively. The cross section for Rb87{\mathrm{Rb}}^{87}Rb87-Ne and Rb87{\mathrm{Rb}}^{87}Rb87-Ar collisions are found to be 1.6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}22}$ cm2{\mathrm{cm}}^{2}cm2 and 9\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}22}$ cm2{\mathrm{cm}}^{2}cm2. These values are in general agreement with values previously obtained by other methods. The extrapolated values of 1T2\frac{1}{{T}_{2}}T2​1​ for zero vapor pressure of rubidium are 185, 237, and 318 ${\mathrm{sec}}^{\ensuremath{-}1}$ for Ne, He, or Ar, respectively. Relaxations by the pumping light or by the magnetic field inhomogeneities are also discussed.
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 $\ensuremath{\sigma}[\ensuremath{\gamma}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{N}})](\mathrm{K}\ensuremath{-}\mathrm{He})=8.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}25}$ cm2{\mathrm{cm}}^{2}cm2 and $\ensuremath{\sigma}[\ensuremath{\gamma}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{S}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{N}})](\mathrm{K}\ensuremath{-}\mathrm{Ne})=141\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}25}$ cm2{\mathrm{cm}}^{2}cm2. The diffusion coefficients of K in He and Ne, corrected to 273 K, are ${D}_{0}(\mathrm{K}\ensuremath{-}\mathrm{He})=0.35$ cm2{\mathrm{cm}}^{2}cm2 ${\mathrm{sec}}^{\ensuremath{-}1}$ and ${D}_{0}(\mathrm{K}\ensuremath{-}\mathrm{Ne})=0.19$ cm2{\mathrm{cm}}^{2}cm2 ${\mathrm{sec}}^{\ensuremath{-}1}$. 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.
We report studies of the magnetic decoupling of Rb spin relaxation in the presence of H2{\mathrm{H}}_{2}H2​ buffer gas at high pressures (> 1.5atm).(>~1.5\mathrm{atm}).(> 1.5atm). At low Rb number densities $(<~5\ifmmode\times\else\texttimes\fi{}{10}^{13}{\mathrm{cm}}^{\ensuremath{-}3}),$ we find that the observed magnetic-field dependence of the spin relaxation is almost solely due to binary collisions between Rb atoms and hydrogen molecules, and that it is very well described by three rates: the Rb-Rb spin-exchange rate, the S-damping rate, and the Carver rate associated with the hyperfine pressure-shift interaction in collisions of Rb with H2{\mathrm{H}}_{2}H2​ molecules. At higher Rb densities, the contribution to the relaxation from Rb triplet dimers becomes significant.