Multiple packets of neutral molecules revolving for over a mile.

The level of control that one has over neutral molecules in beams dictates their possible applications. Here we experimentally demonstrate that state-selected, neutral molecules can be kept together in a few mm long packet for a distance of over one mile. This is accomplished in a circular arrangement of 40 straight electrostatic hexapoles through which the molecules propagate over 1000 times. Up to 19 packets of molecules have simultaneously been stored in this ring structure. This brings the realization of a molecular low-energy collider within reach.

Predissociation of the A2Sigma+ (v' = 3) state of the OH radical.

Predissociation of electronically excited OH A(2)Sigma(+) (v' = 3) is studied using velocity-map imaging of the atomic oxygen photofragments. Fine structure yields, angular distributions and alignment parameters are obtained for the O((3)P(J)), J = 2,1,0 products. Angular distributions for the O(3)P(0) (J = 0) fragment, which has no angular momentum polarization, agree well with predictions from the angular distribution simulation computer routine by Kim et al. [J. Chem. Phys., 2006, 125, 133316] which calculates the anisotropy of photofragment recoil as a function of dissociation lifetime, excitation frequency, rotational level, and rotational constant. When angular momentum polarization (i.e. non-equilibrium population distributions of the magnetic sublevels) of the atomic fragments is present, the polarization sensitivity of the O((3)P(J)) (2 + 1) resonance enhanced multiphoton ionization (REMPI) detection scheme used to detect the O((3)P(2,1)) products affects the measured angular distribution. Strong polarization effects are observed for the O((3)P(2,1)) products and accounted for in a simple sudden limit model for the photodissociation. In agreement with the sudden limit predictions for pre-dissociation of OH A(2)Sigma(+) (v' = 3) through the (4)Sigma(-) state, strongly aligned O((3)P(2)) is found to be the major product.

Photodissociation of vibrationally excited SH and SD radicals at 288 and 291 nm: the S(1D2) channel.

Ultraviolet photodissociation of SH (X 2Pi, upsilon"=2-7) and SD (X 2Pi, upsilon"=3-7) has been studied at 288 and 291 nm, using the velocity map imaging technique to probe the angular and speed distributions of the S(1D2) products. Photodissociation cross sections for the A 2Sigma+<--X 2Pi(upsilon") and 2Delta<--X 2Pi(upsilon") transitions have been obtained by ab initio calculations at the CASSCF-MRSDCI/aug-cc-pV5Z level of theory. Both the experimental and theoretical results show that SH/SD photodissociation from X 2Pi (upsilon"

(2+1) resonance-enhanced ionization spectroscopy of a state-selected beam of OH radicals.

A state-selected beam of hydroxyl radicals is generated using a pulsed discharge source and hexapole field. The OH radicals are characterized by resonance-enhanced multiphoton ionization (REMPI) spectroscopy via the nested D 2Sigma- and 3 2Sigma- Rydberg states. Simplified spectra are observed from the selected |MJ|=3/2 component of the upper Lambda-doublet level of the lowest rotational state (J=32) in ground (v"=0) and excited (v"=1-3) vibrational levels of the OH X 2Pi3/2 state. Two-photon transitions are observed to the D 2Sigma-(v'=0-3) and 3 2Sigma-(v'=0,1) vibronic levels, extending previous studies to higher vibrational levels of the Rydberg states. Spectroscopic constants are derived for the Rydberg states and compared with prior experimental studies. Complementary first-principle theoretical studies of the properties of the D 2Sigma- and 3 2Sigma- Rydberg states [see M. P. J. van der Loo and G. C. Groenenboom, J. Chem. Phys. 123, 074310 (2005), following paper] are used to interpret the experimental findings and examine the utility of the (2+1) REMPI scheme for sensitive detection of OH radicals.

Longitudinal focusing and cooling of a molecular beam.

A neutral polar molecule experiences a force in an inhomogeneous electric field. This electric field can be designed such that a beam of polar molecules is exposed to a harmonic potential in the forward direction. In this potential the longitudinal phase-space distribution of the ensemble of molecules is rotated uniformly. This property is used to longitudinally focus a pulsed beam of ammonia molecules and to produce a beam with a longitudinal velocity spread of 0.76 m/s, corresponding to a temperature of 250 mu K.

Alternate gradient focusing and deceleration of a molecular beam.

Neutral dipolar molecules can be decelerated and trapped using time-varying inhomogeneous electric fields. This has been demonstrated only for molecules in low-field seeking states, but can, in principle, be performed on molecules in high-field seeking states as well. Transverse stability is then much more difficult to obtain, however, since molecules in high-field seeking states always experience a force towards the electrodes. Here we demonstrate that an array of dipole lenses in alternate gradient configuration can be used to maintain transverse stability. A pulsed beam of metastable CO in high-field seeking states is accelerated from 275 to 289 m/s as well as decelerated from 275 to 260 m/s.