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

Abstract

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.

Vibrational relaxation in seeded supersonic alkali halide beams

“…For example, a seeded LiF beam with at least -95% of the molecules in the ground vibration-rotation state can be expected if the relaxation proves to be comparable to that obtained at Chicago for seeded 12 beams. 8 This compares well with the "purity" achieved for alkali halide beams prepared by use of electric resonance state selection, 33 and the seeded salt beam should be several orders of magnitude more intense.…”