Rotationally induced Penning ionization of ultracold photoassociated helium dimers

Abstract

We have studied photoassociation of metastable 2 3 S1 helium atoms near the 2 3 S1-2 3 P2asymptote by both ion detection in a magneto-optical trap and trap-loss measurements in a magnetic trap. A detailed comparison between the results of the two experiments gives insight into the mechanism of the Penning ionization process. We have identified four series of resonances corresponding to vibrational molecular levels belonging to different rotational states in two potentials. The corresponding spin states become quasi-purely quintet at small interatomic distance, and Penning ionization is inhibited by spin conservation rules. Only a weak rotational coupling is responsible for the contamination by singlet spin states leading to a detectable ion signal. However, for one of these series Bose statistics does not enable the rotational coupling and the series detected through trap-loss does not give rise to sufficient ionization for detection.

Effects of non-adiabatic and Coriolis couplings on the bound states of He(23S)+He(23P)

“…Our calculations indicate that very few levels of each series are accessible by photoassociation, implying that the logical inclination to attempt to complete an entire adiabatic series when matching to experimental measurements appears to be invalid. Interestingly, our assignments agree with those of [17] for all levels except those for which we assign two case (c) sets and those with energies of −2.42 GHz and −1.22 GHz.…”

“…Acting as both a level broadening mechanism and a detection method for most experiments, Penning ionization is extremely likely to occur if the bound level possesses singlet or triplet character in its Hund's case (a) basis for R < 20 a 0 . We follow [17] in assuming that this probability is unity for a level with only singlet or triplet short-range character. Although single-channel calculations cannot determine accurately the short-range character of each bound level, Léonard et al [17] have used the absence or presence of different experimental levels to infer the rotational coupling between different case (c) subsets.…”

“…We follow [17] in assuming that this probability is unity for a level with only singlet or triplet short-range character. Although single-channel calculations cannot determine accurately the short-range character of each bound level, Léonard et al [17] have used the absence or presence of different experimental levels to infer the rotational coupling between different case (c) subsets.…”

Prospects for measurement and control of the scattering length of metastable helium using photoassociation techniques

“…In addition, the short-lived singlet and triplet vibrational states effectively merge into a continuum which may result in unwanted background signal during PA experiments. Indeed, long-lived vibrational levels have recently been observed in molecular states which possess quintet character at short internuclear range [12,13]. Some of these states, which are located below the D 2 (2 3 S 1 + 2 3 P 2 ) asymptote, might be useful intermediate levels for a two-laser PA experiment aiming at the determination of the energy of the least-bound level in the scattering potential.…”

Long-range interactions between aHe(2S3)atom and a

“…Recently, there has been considerable interest in the study of helium dimers and ultracold helium collisions associated with metastable helium atoms [1,2,3,4,5,6,7,8,9,10,11].…”