The long-range interaction between an antiprotonic helium atom $\overline{p}{\mathrm{He}}^{+}$ and helium atom in its ground state is studied. We calculate the dispersion coefficients ${C}_{6}$ using the complex coordinate rotation (CCR) formalism in order to comply with the resonant nature of metastable states of the antiprotonic helium. We present as well numerical data on static dipole polarizabilities of antiprotonic helium states. The obtained coefficients ${C}_{6}$ may be used to estimate the collisional shift and broadening of transition lines in a low-density precision spectroscopy of the antiprotonic helium.The long-range interaction between an antiprotonic helium atom $\overline{p}{\mathrm{He}}^{+}$ and helium atom in its ground state is studied. We calculate the dispersion coefficients ${C}_{6}$ using the complex coordinate rotation (CCR) formalism in order to comply with the resonant nature of metastable states of the antiprotonic helium. We present as well numerical data on static dipole polarizabilities of antiprotonic helium states. The obtained coefficients ${C}_{6}$ may be used to estimate the collisional shift and broadening of transition lines in a low-density precision spectroscopy of the antiprotonic helium.

arXiv:1509.06162Physical Review ANov 23, 201512 citations

Temperature Dependence of Helium Metastability Exchange Cross Section

F. D. Colegrove, L. D. Schearer, G. K. Walters

The cross section for exchange of metastability in collisions between ${\mathrm{He}}^{3}$ atoms in the ground ( $1^{1}S_{0}$ ) state and metastable ( $2^{3}S_{1}$ ) state has been measured as a function of temperature by optical pumping techniques. The exchange cross section decreases from about 5.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at 500\ifmmode^\circ\else\textdegree\fi{}K to less than ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$ at 4.2\ifmmode^\circ\else\textdegree\fi{}K. These results suggest a thermally activated exchange process in qualitative agreement with the predicted existence of a long-range repulsive interaction between metastable and ground-state helium atoms as proposed by Buckingham and Dalgarno.The cross section for exchange of metastability in collisions between ${\mathrm{He}}^{3}$ atoms in the ground ($1^{1}S_{0}$) state and metastable ($2^{3}S_{1}$) state has been measured as a function of temperature by optical pumping techniques. The exchange cross section decreases from about 5.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at 500\ifmmode^\circ\else\textdegree\fi{}K to less than ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$ at 4.2\ifmmode^\circ\else\textdegree\fi{}K. These results suggest a thermally activated exchange process in qualitative agreement with the predicted existence of a long-range repulsive interaction between metastable and ground-state helium atoms as proposed by Buckingham and Dalgarno.

Physical ReviewJul 20, 196451 citations

The long-range interaction between an antiprotonic helium atom

\overline{p}{\mathrm{He}}^{+}

and helium atom in its ground state is studied. We calculate the dispersion coefficients

{C}_{6}

using the complex coordinate rotation (CCR) formalism in order to comply with the resonant nature of metastable states of the antiprotonic helium. We present as well numerical data on static dipole polarizabilities of antiprotonic helium states. The obtained coefficients

{C}_{6}

may be used to estimate the collisional shift and broadening of transition lines in a low-density precision spectroscopy of the antiprotonic helium.

The cross section for exchange of metastability in collisions between

{\mathrm{He}}^{3}

atoms in the ground (

1^{1}S_{0}

) state and metastable (

2^{3}S_{1}

) state has been measured as a function of temperature by optical pumping techniques. The exchange cross section decreases from about 5.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}16}$

{\mathrm{cm}}^{2}

at 500\ifmmode^\circ\else\textdegree\fi{}K to less than ${10}^{\ensuremath{-}17}$

{\mathrm{cm}}^{2}

at 4.2\ifmmode^\circ\else\textdegree\fi{}K. These results suggest a thermally activated exchange process in qualitative agreement with the predicted existence of a long-range repulsive interaction between metastable and ground-state helium atoms as proposed by Buckingham and Dalgarno.