Transport and focusing of highly vibrationally excited NO molecules

Complete Quantum State Selectivity in Cold Molecular Beams Using Deflection-Resistant Dark States in a STIRAP Configuration

One of the main goals of chemical dynamics is the creation of molecular beams composed of a single (vibrational, rotational, and magnetic) quantum state of choice. In this Letter, we propose a method to achieve complete quantum state selectivity by producing resistance to electromagnetically induced deflection (EID) and that the state to be selected can be "dialed in" at will. We illustrate the method by showing in detail how to purify thermal beams of the LiRb and IF molecules to yield molecular beams composed of a variety of prechosen single internal quantum states and/or superpositions of such states. We expect that this method will be implemented in all subsequent explorations of the fundamentals of chemical reactions and their control and the use of cold molecules as a vehicle for studying some of the most profound issues of quantum dynamics.

A compact hexapole state-selector for NO radicals

Focusing of molecular beams using an electrostatic hexapole is a mature technique to produce samples of state-selected molecules. The ability to efficiently focus molecules depends on the properties of the molecular species of interest, the length of the hexapole state selector, as well as on the maximum electric field strength that can be achieved in these devices. In particular for species with a small effective dipole moment such as nitric oxide (NO), hexapole state selectors of several meters in length are required to focus the beam. We report on a novel design for an electrostatic hexapole state-selector that allows for a maximum electric field strength of 260 kV/cm, reducing significantly the length of the hexapole that is required to focus the beam. We demonstrate the focusing of a molecular beam of NO radicals (X (2)Π1∕2, v = 0, J = 1∕2, f) using a hexapole of only 30 cm length. A beamstop is integrated inside the hexapole at the geometric center of the device where the molecular trajectories have the largest deviation from the beam axis, effectively blocking the carrier gas of the molecular beam at minimum loss of NO density. The performance of the hexapole state-selector is investigated by state-selective laser induced fluorescence detection, as well as by two-dimensional imaging of the focused packet of NO radicals. The resulting packet of NO radicals has a density of 9 ± 3 × 10(10) cm(-3) and a state purity of 99%.

Cyclic-N3. II. Significant geometric phase effects in the vibrational spectra

An accurate theoretical prediction of the vibrational spectra for a pure nitrogen ring (cyclic-N(3)) molecule is obtained up to the energy of the (2)A(2)/(2)B(1) conical intersection. A coupled-channel approach using the hyperspherical coordinates and the recently published ab initio potential energy surface [D. Babikov, P. Zhang, and K. Morokuma, J. Chem. Phys. 121, 6743 (2004)] is employed. Two independent sets of calculations are reported: In the first set, the standard Born-Oppenheimer approximation is used and the geometric phase effects are totally neglected. In the second set, the generalized Born-Oppenhimer approximation is used and the geometric phase effects due to the D(3h) conical intersection are accurately treated. All vibrational states are analyzed and assigned in terms of the normal vibration mode quantum numbers. The magnitude of the geometric phase effect is determined for each state. One important finding is an unusually large magnitude of the geometric phase effects in the cyclic-N(3): it is approximately 100 cm(-1) for the low-lying vibrational states and exceeds 600 cm(-1) for several upper states. On average, this is almost two orders of magnitude larger than in the previously reported studies. This unique example suggests a favorable path to experimental validation.

Cyclic-N3. I. An accurate potential energy surface for the ground doublet electronic state up to the energy of the 2A2/2B1 conical intersection

A sophisticated adiabatic ground electronic state potential energy surface for a pure nitrogen ring (cyclic-N3) molecule is constructed based on extensive high-level ab initio calculations and accurate three-dimensional spline representation. Most of the important features of the potential energy surface are presented using various reduced dimensionality slices in internal hyperspherical coordinates as well as full dimensional isoenergy surfaces. Very significant geometric phase effects are predicted in the spectra of rotational-vibrational states of cyclic-N3.