The dipole spectrum and properties of helium

Retarded dipole-dipole dispersion interaction potential for helium

“…The retarded potential for a pair of ground-state helium atoms has been calculated by Getzin and Karplus [11],Langhoff [12], and Luo et al [13] In atomic units (a.u. ), which will be used throughout, the potential V(R) is [1,13] With the variable of integration changed to x =2uR a, [14] showed that the potential is insensitive to the details of the effective dipole transitions, as noted by Luo et al [13]in their calculations of the retarded potential. The uncertainty in the results in Table I should be less than one in the fourth significant figures following the leading zeros or nines.…”

Dispersion forces between noble gas atoms

“…5 The starting point of most modern work on dispersion forces is provided by the Casimir-Polder 6 formula, in which the dispersion interaction is expressed as an integral over imaginary frequencies of the appropriate dynamic polarizabilities of the interacting species. Introducing the dynamic multipole polarizability (4) and using the identity…”

“…(9) reduces to the one used by Karplus and Kolker 3 and Chan and Dalgarno. 4 Minimizing the variation functional L with respect to the variation parameters c" ): *(a>), one obtains where the matrices M, and N, are given by (11) (12) (13) Using some simple operator algebra 7 it can be shown that the elements of the matrix M, can be written as…”

“…Substituting the variationally determined functions xî(w) in Eq. (6) 4 noticed that the variation procedure they used automatically ensures that the/-sum rule is satisfied. This also holds for the higher order polarizabilities.…”

“…Therefore it appears that for the evaluation of higher order dispersion forces one has to resort to theoretical methods. In this paper we extend a simple variation procedure first used by Karplus and Kolker 3 and by Chan and Dalgarno 4 for the calculation of the dipole-dipole dispersion interaction between hydrogen and helium, to calculate the dipole-dipole, dipole-quadrupole, quadrupole-quadrupole, and dipole-octupole dispersion forces between helium, neon, and argon.…”