Level structure of deeply bound levels of the c3Σg+ state of Rb2

Abstract

We spectroscopically investigate the hyperfine, rotational and Zeeman structure of the vibrational levels v = 0, 7, 13 within the electronically excited c 3 Σ + g state of 87 Rb 2 for magnetic fields of up to 1000 G. As spectroscopic methods we use short-range photoassociation of ultracold Rb atoms as well as photoexcitation of ultracold molecules which have been previously prepared in several well-defined quantum states of the a 3 Σ + u potential. As a byproduct, we present optical two-photon transfer of weakly bound Feshbach molecules into a 3 Σ + u , v = 0 levels featuring different nuclear spin quantum numbers. A simple model reproduces well the molecular level structures of the c 3 Σ + g vibrational states and provides a consistent assignment of the measured resonance lines. Furthermore, the model can be used to predict the relative transition strengths of the lines. From fits to the data we extract for each vibrational level the rotational constant, the effective spin-spin interaction constant, as well as the Fermi contact parameter and (for the first time) the anisotropic hyperfine constant. In an alternative approach, we perform coupled-channel calculations where we fit the relevant potential energy curves, spin-orbit interactions and hyperfine functions. The calculations reproduce the measured hyperfine level term frequencies with an average uncertainty of ±9 MHz, similar as for the simple model. From these fits we obtain a section of the potential energy curve for the c 3 Σ + g state which can be used for predicting the level structure for the vibrational manifold v = 0 to 13 of this electronic state.

State-to-state chemistry at ultra-low temperature

“…The Rb 2 energy levels are calculated with a coupled-channel model which uses the Hamiltonian for atom pairs of s + s or s + p states (see e.g. (42,43)) and potentials derived from former spectroscopic work of several groups. We have reevaluated the analysis of the singlet and triplet ground states (42) correcting the assignment of some high rotational levels as remarked in (44) and derived improved potentials for X 1 Σ + g and a 3 Σ + u .…”

“…Because the analysis includes a number of Feshbach resonances we obtain reliable predictions for the asymptotic level structure. The potential system for the atom pair s + p was derived from spectroscopic work collected in (38) and work from our own group (39,43).…”