Pulsed rotating supersonic source used with merged molecular beams

TL;DR

This paper presents a pulsed rotating supersonic beam source that produces intense, tunable molecular beams with low background pressure, enabling precise control of collision energies in molecular experiments.

Contribution

The authors developed a pulsed version of a rotating supersonic source, significantly reducing background pressure and allowing for adjustable beam speeds suitable for collision studies.

Findings

Produced molecular beams with speeds as low as 35 m/s and as high as 400 m/s.

Generated intense pulses containing approximately 10^12 to 10^15 molecules.

Enabled low-energy collision experiments by matching beam velocities.

Abstract

We describe a pulsed rotating supersonic beam source, evolved from an ancestral device [M. Gupta and D. Herschbach, J. Phys. Chem. A 105, 1626 (2001)]. The beam emerges from a nozzle near the tip of a hollow rotor which can be spun at high-speed to shift the molecular velocity distribution downward or upward over a wide range. Here we consider mostly the slowing mode. Introducing a pulsed gas inlet system, cryocooling, and a shutter gate eliminated the main handicap of the original device, in which continuous gas flow imposed high background pressure. The new version provides intense pulses, of duration 0.1-0.6 ms (depending on rotor speed) and containing ~10^12 molecules at lab speeds as low as 35 m/s and ~ 10^15 molecules at 400 m/s. Beams of any molecule available as a gas can be slowed (or speeded); e.g., we have produced slow and fast beams of rare gases, O2, Cl2, NO2, NH3, and SF6. For collision experiments, the ability to scan the beam speed by merely adjusting the rotor is especially advantageous when using two merged beams. By closely matching the beam speeds, very low relative collision energies can be attained without making either beam very slow.