Spectra of ultracold KRb molecules in near-dissociation vibrational levels

Abstract

We have studied resonance-enhanced two-photon ionization of ultracold 39K85Rb molecules in highly excited long-range vibrational levels of the X 1Σ+ and a 3Σ+ states. These molecules are formed by photoassociation (PA) of ultracold 39K and 85Rb atoms, followed by spontaneous emission to the X 1Σ+ and a 3Σ+ states. In the range 15 500–17 200 cm−1, we observe many intermediate and long-range levels of the previously unobserved 4 3Σ+ and 4 1Σ+ states and evidence for the onset of the previously unobserved 3 3Π state. The observed vibrational spectra of these states are in very good agreement with calculated vibrational levels based on the ab initio potentials of Rousseau, Allouche and Aubert-Frécon. Such experiments illustrate some of the unique advantages of using PA-produced ultracold molecules for investigation of long-range vibrational levels and long-range forces, and for unravelling dense spectra because only a few rotational levels are populated.