Modeling Photoassociative Spectra of Ultracold NaK + K.

A model for photoassociation of ultracold atoms and molecules is presented and applied to the case of K and NaK bosonic particles. The model relies on the assumption that photoassociation is dominated by long-range atom-molecule interactions well outside the chemical bond region. The frequency of the photoassociation laser is chosen close to a bound-bound rovibronic transition from the Σ ground state toward the metastable Π lowest excited state of NaK, allowing us to neglect any other excitation, which could hinder the photoassociation detection.

Strong ortho/para effects in the vibrational spectrum of Cl(H).

The predissociation spectrum of the Cl-35(H) complex is measured between 450 and 800 cm in a multipole radiofrequency ion trap at different temperatures using the FELIX infrared free electron laser. Above a certain temperature, the removal of the Cl(p-H) para nuclear spin isomer by ligand exchange to the Cl(o-H) ortho isomer is suppressed effectively, thereby making it possible to detect the spectrum of this more weakly bound complex. At trap temperatures of 30.

Nuclear spin conservation enables state-to-state control of ultracold molecular reactions.

Quantum-state control of reactive systems has enabled microscopic probes of underlying interaction potentials and the alteration of reaction rates using quantum statistics. However, extending such control to the quantum states of reaction outcomes remains challenging. Here, we realize this goal by utilizing the conservation of nuclear spins throughout the reaction.

Optical Shielding of Destructive Chemical Reactions between Ultracold Ground-State NaRb Molecules.

We propose a method to suppress the chemical reactions between ultracold bosonic ground-state ^{23}Na^{87}Rb molecules based on optical shielding. By applying a laser with a frequency blue-detuned from the transition between the lowest rovibrational level of the electronic ground state X^{1}Σ^{+}(v_{X}=0,j_{X}=0), and the long-lived excited level b^{3}Π_{0}(v_{b}=0,j_{b}=1), the long-range dipole-dipole interaction between the colliding molecules can be engineered, leading to a dramatic suppression of reactive and photoinduced inelastic collisions, for both linear and circular laser polarizations. We demonstrate that the spontaneous emission from b^{3}Π_{0}(v_{b}=0,j_{b}=1) does not deteriorate the shielding process.

Direct observation of bimolecular reactions of ultracold KRb molecules.

Femtochemistry techniques have been instrumental in accessing the short time scales necessary to probe transient intermediates in chemical reactions. In this study, we took the contrasting approach of prolonging the lifetime of an intermediate by preparing reactant molecules in their lowest rovibronic quantum state at ultralow temperatures, thereby markedly reducing the number of exit channels accessible upon their mutual collision. Using ionization spectroscopy and velocity-map imaging of a trapped gas of potassium-rubidium (KRb) molecules at a temperature of 500 nanokelvin, we directly observed reactants, intermediates, and products of the reaction KRb + KRb → KRb* → K + Rb Beyond observation of a long-lived, energy-rich intermediate complex, this technique opens the door to further studies of quantum-state-resolved reaction dynamics in the ultracold regime.