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The Duration of Hydrogen Atom Spin Exchange Collisions

S. B. Crampton, H. T. M. Wang

peacJan 1, 19750 citations

Collision frequency shift of hyperfine transitions in atomic hydrogen at a low temperature

A. I. Safonov, I. I. Safonova, I. I. Lukashevich

The experimental results on the collision frequency shift of ESR in diluted two-and three-dimensional atomic hydrogen at ultralow temperature have been analyzed. The apparent contradiction between experiment and theory is resolved by taking into account the relation between the symmetry of the state of two atoms and their total electron spin S . For example, transitions between symmetric and antisymmetric states of a pair of atoms induced by a symmetric perturbation are forbidden. If symmetric and antisymmetric states are, respectively, pure electronic triplets ( S = 1) and singlets ( S = 0), this results in the cancellation of the singlet-triplet transitions. Thus, the collision frequency shift of b → c and b → a transitions vanishes in a completely electron and nuclear spin-polarized gas (hyperfine state b ). The comparison is performed with experiments in ultracold alkali vapors.The experimental results on the collision frequency shift of ESR in diluted two-and three-dimensional atomic hydrogen at ultralow temperature have been analyzed. The apparent contradiction between experiment and theory is resolved by taking into account the relation between the symmetry of the state of two atoms and their total electron spin S . For example, transitions between symmetric and antisymmetric states of a pair of atoms induced by a symmetric perturbation are forbidden. If symmetric and antisymmetric states are, respectively, pure electronic triplets ( S = 1) and singlets ( S = 0), this results in the cancellation of the singlet-triplet transitions. Thus, the collision frequency shift of b → c and b → a transitions vanishes in a completely electron and nuclear spin-polarized gas (hyperfine state b ). The comparison is performed with experiments in ultracold alkali vapors.

Journal of Experimental and Theoretical Physics LettersJan 1, 20089 citations

Hyperfine and Zeeman interactions in ultracold collisions of molecular hydrogen with atomic lithium

Hubert Jóźwiak, Timur V. Tscherbul, Piotr Wcisło

We present a rigorous quantum scattering study of the effects of hyperfine and Zeeman interactions on cold Li-H2 collisions in the presence of an external magnetic field using a recent ab initio potential energy surface. We find that the low-field-seeking states of H2 predominantly undergo elastic collisions: the ratio of elastic-to-inelastic cross sections exceeds 100 for collision energies below 100 mK. Furthermore, we demonstrate that most inelastic collisions conserve the space-fixed projection of the nuclear spin. We show that the anisotropic hyperfine interaction between the nuclear spin of H2 and the electron spin of Li can have a significant effect on inelastic scattering in the ultracold regime, as it mediates two processes: the electron spin relaxation in lithium and the nuclear spin-electron spin exchange. Given the predominance of elastic collisions and the propensity of inelastic collisions to retain H2 in its low-field-seeking states, our results open up the possibility of sympathetic cooling of molecular hydrogen by atomic lithium, paving the way for future exploration of ultracold collisions and high-precision spectroscopy of H2 molecules.We present a rigorous quantum scattering study of the effects of hyperfine and Zeeman interactions on cold Li-H2 collisions in the presence of an external magnetic field using a recent ab initio potential energy surface. We find that the low-field-seeking states of H2 predominantly undergo elastic collisions: the ratio of elastic-to-inelastic cross sections exceeds 100 for collision energies below 100 mK. Furthermore, we demonstrate that most inelastic collisions conserve the space-fixed projection of the nuclear spin. We show that the anisotropic hyperfine interaction between the nuclear spin of H2 and the electron spin of Li can have a significant effect on inelastic scattering in the ultracold regime, as it mediates two processes: the electron spin relaxation in lithium and the nuclear spin-electron spin exchange. Given the predominance of elastic collisions and the propensity of inelastic collisions to retain H2 in its low-field-seeking states, our results open up the possibility of sympathetic cooling of molecular hydrogen by atomic lithium, paving the way for future exploration of ultracold collisions and high-precision spectroscopy of H2 molecules.

arXiv:2312.13652The Journal of Chemical PhysicsMar 5, 20242 citations

The Role of Electron Spin in Atomic Collisions

Wolfgang Jitschin

NATO ASI series. Series B : PhysicsJan 1, 19850 citations

Spin flipping collisions of hydrogen atoms

Bernard Zygelman

Bulletin of the American Physical SocietyMay 27, 20100 citations

Nuclear-Spin Effects Are Important in Analyzing Spin-Exchange Experiments

Hyatt M. Gibbs

Lambert's proof that the inclusion of nuclear spin does not alter the equation of motion for the electronic polarization is shown to be valid only when the hyperfine interaction is negligible. Usually the hyperfine frequency is much greater than the frequency of spin-exchange collisions; then the effect of the hyperfine interaction between collisions invalidates Lambert's proof. In general, spin exchange with a second depolarized species relaxes the electronic polarization as the sum of two exponentials, as shown by Gibbs and Grosset\^ete.Lambert's proof that the inclusion of nuclear spin does not alter the equation of motion for the electronic polarization is shown to be valid only when the hyperfine interaction is negligible. Usually the hyperfine frequency is much greater than the frequency of spin-exchange collisions; then the effect of the hyperfine interaction between collisions invalidates Lambert's proof. In general, spin exchange with a second depolarized species relaxes the electronic polarization as the sum of two exponentials, as shown by Gibbs and Grosset\^ete.

Physical Review AJan 1, 19715 citations

Spin exchange taking into account hyperfine coupling between electron and nuclear spins during a collision: I. Collisional dynamics of hydrogen-like atoms

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