Steven Hoekstra

Near-threshold inelastic collisions using molecular beams with a tunable velocity

Molecular scattering behavior has generally proven difficult to study at low collision energies. We formed a molecular beam of OH radicals with a narrow velocity distribution and a tunable absolute velocity by passing the beam through a Stark decelerator. The transition probabilities for inelastic scattering of the OH radicals with Xe atoms were measured as a function of the collision energy in the range of 50 to 400 wavenumbers, with an overall energy resolution of about 13 wavenumbers. The behavior of the cross-sections for inelastic scattering near the energetic thresholds was accurately measured, and excellent agreement was obtained with cross-sections derived from coupled-channel calculations on ab initio computed potential energy surfaces.

The radiative lifetime of metastable CO (a (3)Pi, v=0)

We present a combined experimental and theoretical study on the radiative lifetime of CO in the a (3)Pi(1,2), v=0 state. CO molecules in a beam are prepared in selected rotational levels of this metastable state, Stark-decelerated, and electrostatically trapped. From the phosphorescence decay in the trap, the radiative lifetime is measured to be 2.63+/-0.03 ms for the a (3)Pi(1), v=0, J=1 level. From the spin-orbit coupling between the a (3)Pi and the A (1)Pi states a 20% longer radiative lifetime of 3.16 ms is calculated for this level. It is concluded that coupling to other (1)Pi states contributes to the observed phosphorescence rate of metastable CO.

Laser-cooled RaF as a promising candidate to measure molecular parity violation

The parameter W{sub a}, which characterizes nuclear-spin-dependent parity violation (PV) in the molecular spin-rotational Hamiltonian, was computed with a quasirelativistic Hartree-Fock approach for radium fluoride (RaF) and found to be one of the largest absolute values predicted so far. The peculiar electronic structure of RaF leads to highly diagonal Franck-Condon matrices between the energetically lowest two electronic states, which qualifies RaF for direct laser cooling. A subset of diatomic molecules with a wide range of internal structures suitable for this cooling technique is also indicated. As trapped cold molecules offer superior coherence times, RaF can be considered promising for high-precision experiments aimed at molecular PV.

Electrostatic trapping of metastable nh molecules

We report on the Stark deceleration and electrostatic trapping of

Production and deceleration of a pulsed beam of metastable NH (alpha(1)Delta) radicals

^{14}\text{N}\text{H}

A new approach to test Lorentz invariance

(a^{1}\ensuremath{\Delta})

Optimizing the Stark-decelerator beamline for the trapping of cold molecules using evolutionary strategies

radicals. In the trap, the molecules are excited on the spin-forbidden

Loading Stark-decelerated molecules into electrostatic quadrupole traps

A^{3}\ensuremath{\Pi}\ensuremath{\leftarrow}a^{1}\ensuremath{\Delta}

Preparation of an ultra-cold sample of ammonia molecules for precision measurements

transition and detected via their subsequent fluorescence to the