Ab Initio Spin−Orbit Configuration Interaction Calculations for High-Lying States of the HeNe Quasimolecule

Abstract

Multireference configuration interaction (MRD-CI) calculations are reported for a large series of electronic states of the HeNe quasimolecule up to 170000 cm(-1) excitation energy, including those that dissociate to the 3S1 and 2 1S0 excited states of the He atom. Spin-orbit coupling is included through the use of relativistic effective core potentials (RECPs). Good agreement is obtained with experimental spectroscopic data for the respective atomic levels, although there is a tendency to systematically underestimate the energies of the Ne atom by 1000-1500 cm(-1) because of differences in the correlation effects associated with its ground and Rydberg excited states. Potential curves are calculated for each of these states, and a number of relatively deep minima are found. The CI Omega-state wave functions are sufficiently diabatic until r = 4-5 a0 to allow for a clear identification of the He 1s-2s excited states. Electric dipole transition moments are computed between these states and the HeNe X 0+ ground state up to r = 4.0 a0, and it is found that the 2 (1)S0 - X maximum value is over an order of magnitude larger than that for the corresponding (3)S1 - X excitation process.

Ab initio study of the lifetime of weakly bound He(21S)–Ne molecules

“…The reaction (1) is the basis for the first gas laser and seems to be one of the most extensively studied excitation transfer cases in atomic collision physics. In principle, there is an alternative pathway for the depopulation of metastable Heð2 1 SÞ atoms in collisions with surrounding Ne atoms, namely the collision-induced process [2]: Heð2 1 SÞ þ Neð2p 6 1 SÞ ! Heð1 1 SÞ þ Neð2p 6 1 …”

“…More precisely, an atomic interaction destroys the spherical symmetry of the helium atom in the metastable state via admixture of p-atomic states with the zeroeth projection of the electric moment on the molecular axis. Although the first semi-empirical estimate of the dipole moment in the 5-8 a 0 region was given long ago [3], ab initio calculations of the corresponding potential energies and the transition dipole moments have been performed only recently [4].…”

“…Recent ab initio calculations [4] have revealed the existence of a potential well at short interatomic distances and a potential barrier which can be qualitatively described as a consequence of avoided crossings of molecular 0 þ states produced by two sets of diabatic states correlating at large distances with Heð2 1 SÞÀNe and Heð1 1 SÞÀNeð5s, 4d, 4f Þ atoms. Thus, the question about the lifetime of bound molecular states correlating with the atomic metastable state Heð2 1 SÞ state arises quite naturally.…”

“…Thus, the question about the lifetime of bound molecular states correlating with the atomic metastable state Heð2 1 SÞ state arises quite naturally. The present paper addresses this question by performing the first calculation of the lifetime for the weakly bound Heð2 1 SÞÀNe molecule in its lowest vibrational state based on the improved recent quantum chemical data [4].…”

Long-range interactions of excited He atoms with ground-state noble-gas atoms

“…The collision processes include Penning ionization [1][2][3][4][5], associative ionization [2], and the formation of quasimolecules [6][7][8], which are of great importance in many areas of physics, such as gaseous lasers, low-temperature plasmas, astrophysics, and radiation physics. The excited noble-gas atoms can be metastable atoms, optically allowed excited atoms [9], or Rydberg atoms [10][11][12] such as He(14 1 P , 15 1 …”