Review pubs.acs.org/CR
Toward State-to-State Dynamics in Ultracold Collisions: Lessons from High-Resolution Spectroscopy of Weakly Bound Molecular Complexes David J. Nesbitt* JILA, National Institute of Standards and Technology, and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, United States ing diatomic molecule.7,10−15 From a chemical physics perspective, these diatomic molecules might be considered as relatively arcane objects, with mean bond lengths of many thousands of angstroms and energies only a few megahertz (i.e., a few nano eV) below the dissociation limit.7,8,16 However, the fact that such pairs of separated atoms are formed with center of mass velocities corresponding to sub-microkelvin temperatures and therefore essentially stationary in the laboratory frame is both extremely elegant and intellectually compelling. Indeed, this novel experimental platform of molecules near the dissociation limit offers a fundamentally new and exciting arena for studying three body interactions and ultra low energy atomic collision dynamics. CONTENTS Although such ultraweakly chemically interacting species 1. Introduction 5062 might not seem an obvious fit for a Chemical Reviews thematic 2. Experimental Section 5064 issue, recent advances in this rapidly emerging field of ultracold 3. High-Resolution IR Spectroscopy of van der molecules are now providing a critical change in this way of Waals Complexes: Ultranarrow versus Ultracold thinking.17−26 In particular, there have been pioneering efforts Collisional Resonance Dynamics 5064 in a number of laboratories,1,4,21−23,26−30 which have now 3.1. Extreme Complex Metastability at E ≫ D0 5064 convincingly demonstrated optical conversion of these highly 3.2. Ultracold Vibrational Feshbach Resonances 5066 vibrationally excited molecules into deeply chemically (or in 3.3. Ultracold Internal Rotor Feshbach Resonansome cases repulsively)29 bound species in the ground vibronic ces: “Molecular Baseball” 5066 state. Of special relevance to the field of ultracold chemistry 3.4. Ultracold Internal Rotor Shape Resonances 5067 have been methods by DeMille, Jin, and Ye for optically 3.5. From Atom + Diatom to Polyatomic Resoforming the ground vibronic state of ultracold polar molecules nances: Dynamics versus Statistics 5068 (e.g., RbCs and KRb), based on laser photoassociation of 4. Potential Lessons for Ultracold Chemical Reacultracold atoms followed by Raman pumping into the lowest tion Dynamics 5068 vibrational level.21,22,26,31 Indeed, particularly critical has been 5. Summary and Conclusion 5070 the development of fully coherent Raman methods by Jin and Author Information 5071 Ye for laser manipulation of ultracold K and Rb atom pairs to Corresponding Author 5071 (i) form the lowest vibrational, rotational, and even hyperfine Notes 5071 state of the KRb diatomic by (ii) expelling this excess energy Biography 5071 away in the form of a single anti-Stokes Raman photon (for Acknowledgments 5071 40 87 K Rb, D0 ≈ 4180.52 cm−1), and thereby (iii) leaving a References 5071 chemically reactive, ground-state molecule nearly motionless in the laboratory frame.21−23 What is especially powerful about these coherent Raman 1. INTRODUCTION advances is that the transformation process is essentially 100% There has been spectacular progress over the past decade in the efficient, which permits sufficiently high real space densities use of narrow laser excitation of gases with Doppler recoil of (1011−1012 #/cm3) of diatomic reactants to be collocated for the resonantly scattered photons to cool atoms to microkelvin ultracold (200−900 nK) collisions over sufficiently long temperatures or lower, typically designated as the “ultracold” optimal trap lifetimes (
