Nuclear Magnetic Resonance of Diatomic Alkali Molecules in Optically Pumped Alkali Vapors

Abstract

NMR signals from diatomic alkali molecules have been observed in optically pumped cesium and rubidium vapors. The nuclear relaxation times were found to be strongly dependent on the temperature and buffer-gas pressure. The relaxation time seems to be determined by at least two and possibly three major factors: motional narrowing of the molecular hyperfine structure, breakup of the diatomic molecules by collisions with buffer-gas atoms, and possibly chemical exchange of free atoms with atoms bound in the molecules.Recently, Nienstadt et al} have used the chargeexchange method of Mitchell and Fortson 2 to make precision measurements of the Cs + NMR frequency in optically pumped cesium vapor. During the course of this work Nienstadt et al} noticed that NMR signals could still be observed even when no Cs + ions were intentionally produced in the vapor. They remarked that they "do not exclude the possibility that it [the signal] is associated with NMR in the Cs 2 molecule." We have observed similar NMR signals in optically pumped cesium and rubidium, and we present data which indicate that the signals do indeed originate in diatomic alkali molecules. The behavior of the molecules is strongly affected by the temperature and buffer-gas pressure, and these experiments afford a unique and simple way to observe simple gas-phase chemical reaction rates for a system in thermal equilibrium. These seem to be the first measurement of the formation and breakup rates of alkali molecules. The molecules also represent a new factor which must be taken into consideration when designing miniature optically pumped devices for operation at high temperature. 3 Our data were obtained with the apparatus sketched in Fig.

Magnetic shielding and spin-rotation interaction in ground state alkali molecules

“…The resonance cell is filled with the enriched isotopes 8SRb or 8VRb. Contrary to 39K 2 the linewidths of the nmr signals in 85Rb 2 and 87Rb 2 are decreasing with increasing Ne density in agreement with [4]. The linewidths (FWHM) always exceed 1,000 Hz for SSRb 2 and 1,500 Hz for 87Rb 2.…”

Magnetic shielding studies on the alkali molecules Na2 and Cs2 by NMR

“…The linewidths (FWHA) of the NMR in Cs 2 and Na 2 are about the same (300 Hz). Relaxation studies on Cs 2 [17,21,23] and Na 2 [19] have shown that there are three relaxation processes that contribute to the linewidth. These are the atom-molecule exchange reaction X + Xz---,X 2 + X, the dissociation X 2 + B~X + X +B of an alkali molecule X 2 by an buffer gas collision (buffer gas atom B), and the intramolecular relaxation which is due to the hyperfine coupling between nuclear spins and molecular rotation.…”

Collision induced dissociation of Cs2 studied by atom-molecule-exchange optical pumping

“…A special control unit is used, which turns off and on the rf field during several adjustable time intervals r. The signal following each pulse is monitored in the transmitted light and sampled by a multichannel analyzer over a time A. Thus each address of this multichannel analyzer is assigned to the signal with a defined pulse length r. The resulting curve is the function S(z) of Equation (8). In Figure 1 the result of such a measurement of S(r) is shown.…”

“…The atom-molecule exchange optical pumping method is used, which is already reported on in previous papers [7,8]. A resonance cell, containing an alkali vapor and a buffer gas is illuminated by circularly polarized resonance radiation.…”