Velocity Distributions in Molecular Beams from Nozzle Sources

Abstract

The velocity distributions in molecular beams of argon produced by the Kantrowitz-Grey supersonic nozzle technique have been investigated using a time-of-flight method. It is shown that the transition from continuum to free molecular flow in free jet expansion limits the minimum width of the velocity distribution which may be obtained. The Mach number corresponding to the axial velocity distribution of the expanding gas approaches a limit which varies inversely with the two-fifths power of the Knudsen number at the nozzle. With argon at room temperature the narrowest velocity distribution obtained corresponds to a Mach number of 23 (90% of the molecules within 5.4% of the most probable velocity).

Gas-Phase IR Spectroscopy of Nucleobases

“…Gas-phase spectroscopy of neutral molecules, as opposed to ions, usually involves the use of supersonic molecular beams (1)(2)(3)(4). For smaller compounds this can be achieved by seeding in the inert drive gas.…”

“…Collision free conditions in vacuo provide insight in the intrinsic properties of individual molecules, free of any interactions. Without such isolation many fundamental properties can be masked by the biological environment, such 2 as the macromolecular structure of the double helix, base pairing interactions, and the role of the solvent. Among the properties of interest are conformational preferences, tautomeric population distributions, hydrogen bonded and pi-stacking structures, inter-and intra molecular interactions, and excited state dynamics.…”

Scattering of thermal He beams by crossed atomic and molecular beams. II. The He–Ar van der Waals potential

“…Although optimum operating conditions could be estimated theoretically for these beam sources, 32 • 35 the approximations involved make it worthwhile, in addition to design calculations, to perform experimental optimization studies. For the primary beam, it was generally found in these studies that intensity maximization and velocity spread minimization (with respect to gas inlet pressure and nozzle-skimmer separation) were complementary characteristics, while the beam angular spread was independent of these variables.…”

“…The primary beam (PB) is of the supersonic design, 32 with nozzle (Nz) and skimmer (Sk) diameters of 0. 07 and 0.…”

Scattering of thermal He beams by crossed atomic and molecular beams. IV. Spherically symmetric intermolecular potentials for He+CH4, NH3, H2O, SF6

“…5 and an "effective" specific heat ratio of 1. 64, 13 indicating only very slight cooling of internal states; thus the rotational temperature is presumably close to the ambient one {298 K).…”