A High Intensity Source for the Molecular Beam. Part I. Theoretical

Abstract

In a standard molecular beam source the maximum attainable intensity in the collimated beam is limited first by the effusion rate through the oven slit, which must be made sufficiently narrow to attain free molecule flow, and second by unfavorable geometrical factors encountered in selecting a collimated beam from random initial velocities. This paper will propose that the first slit be placed in the flow from a miniature high velocity nozzle coaxial with the final beam. The nozzle converts part (∼¾ for a Mach number of 4 in the design for air to be presented) of the random translational and internal energy of the oven gas into directed mass motion. The mass motion provides an initial rough collimation, which improves both the effusion rate and the geometrical factors, indicating a considerable possible beam intensification (by a factor of ∼75 in the sample design). The velocities of the molecules in the final beam are grouped about the initial mass velocity which provides a partial velocity selection. In this paper a theoretical design study and estimates of performance of this type of source are given.

High Pressure (>1 atm) Electrospray Ionization Mass Spectrometry

“…Here, instead of raising the pressure directly around the ion inlet of the mass spectrometer, the high pressure ion source was separated from the first pumping stage with an additional stage at near atmospheric pressure. The arrangement is like a nozzle-skimmer system [10], where the ions exit from the high pressure stage via a nozzle to an open space at~1 atm and re-enter to the vacuum through the ion sampling skimmer.…”

Serendipitous Meanderings and Adventures With Molecular Beams

“…As a young graduate student, I was not aware of the pioneering experiments on atomic and molecular scattering conducted in Hamburg during the period 1926 to 1933 in Otto Stern's laboratory (6). But Kantrowitz's & Grey's 1951 paper (7), suggesting the use of nozzle beams, and the subsequent unsuccessful attempt by Kistiakowsky & Slichter (8) constructing a molecular-beam machine. As Greene later told me, they had already thought about doing something new in addition to shock waves (Greene) and studying transport processes (Ross).…”

IN MY TIME: Scenes of Scientific Life

“…This section was headed by the French Alsatian Herman Hering, a man of great rigor who had survived a German concentration camp, and later by the excellent British chemist Jack Sutton. Since they had plenty of funding, I suggested that their new young scientist, Roger Campargue, should build a true molecular beam of the Kantrowitz & Grey type (93) and cross it with a controlled electron beam so as to do improved spectroscopic experiments, on cold supersonic molecular beams, with respect to my Orsay effusion devices. Campargue built the molecular beam but, to my increasing frustration, never did the crossed beam experiment.…”