Focusing of polar molecules in an electrostatic quadrupole: the use of a collimating orifice to remove the direct beam

Beams of CsF in selected vibrational (v=0,1,2,3,4) and rotational (J,M=1,0) states, with narrow velocity distributions, have been produced via an improved microwave molecular beam electric resonance (MBER) method utilizing ’’displacement focusing.’’ The apparatus consists of an effusive graphite oven source, a slotted-disk velocity selector, and two electrostatic quadrupole fields. The first field focuses the (J,M) = (2,0) state through an off-axis collimating orifice into a microwave cavity. Here microwave radiation stimulates the J=2→1 transition for a specified v state. Then a second (’’refocusing’’) quadrupole delivers the specified (v,J,M) = (v,1,0) state to an image point (a collimated surface ionization mass filter detector). The final focused and state-selected beam, say (0,1,0), has a purity ≳95% with respect to J,M. However, the best over-all (v,J,M) state purity achieved was 83% (0,1,0), with 17% of ’’background’’ [of which 4% is actually (0,1,0), 4% is (1,1,0), 4% (v,1,0) with v?2, and the remaining 5% unselected (scattered) CsF]. Using the present effusive oven source, the best intensity achieved for a state-selected (0,1,0) beam (of velocity 3.65×104 cm sec−1) was 1×105 molecule sec−1, corresponding to a flux density of 1.3×109 molecule cm−2 sec−1.

Pure-state molecular beams: Production of rotationally, vibrationally, and translationally selected CsF beams

Bromberg

Proctor

Bernstein

1975

Detection of LiH and NaH molecular beams by laser fluorescence and measurement of radiative lifetimes of the A 1Σ+ state

Dagdigian

1976

Radiative and nonradiative lifetimes for vibrational levels of the A 1Σ+ state of 7LiHWe report here detection of supersonic molecular beams of LiH and NaH using the tunable laser fluorescence technique. From measurement of the relative intensities of individual rotational lines in the excitation spectrum. beam rotational temperatures T mt = 600± 100'K for LiH and T mt = 230± 50'K for NaH have been obtained. Direct measurement of the fluorescence decay of excited A I~+ state molecules after pulsed laser excitation has allowed determination of the radiative lifetimes of several.3, and r(v' =7,1' = l2)=36.9±1.9 nsec for 7LiH and r( v' = 8,1' = 3) = 22.7 ± 1.6 nsec for 23NaH, where the quoted uncertainties represent three standard deviations. These values agree to within the ~ 10% quoted experimental uncertainties with theoretical lifetimes calculated using ab initio electronic transition moments of Docken and Hinze (LiH) and Sachs, Hinze. and Sabelli (NaH). Molecular fluorescence is excited by a homebuilt pulsed (10 pps) tunable nitrogen-laser-pumped dye laser. The nitrogen laser is very similar in design to the "midsize" laser (nominal 300 kW peak power) described by Woodward, Ehlers, and Lineberger. 8 Rather than machining a circular discharge tube, a rectangular tube was constructed by cementing a pair of flat alumi-

Polarized, rotationally state-selected cross sections and anisotropic intermolecular potentials for LiF on Ar

Tsou

Auerbach

Wharton

1979

High resolution differential cross sections of LiF in the J=1 rotational state in both a polarized condition and an unpolarized condition were experimentally studied with an Ar target for a range of LiF energies from 0.3 to 1.9 eV. The technique for performing such experiments is described in detail, including a description of the high resolution state selector and the seeded supersonic source. High frequency and rainbow features are observed in the differential cross sections. Manifestations of these oscillations are also observed in the significant difference in cross section due to polarization. The infinite order sudden approximation was used in a preliminary way to interpret the data. A model potential was used that had an inverse radial power series and appropriate angular dependent Legendere polynomials. The differential cross section is sensitive to the anisotropy parameters chosen. The cross section is generally larger for the (J, M) = (1, 1) polarization along the relative velocity for the energies and the small angles observed here.