THE SCATTERING OF A POTASSIUM ATOMIC BEAM BY A CROSSED BEAM OF BROMINE MOLECULES
A study was made of the scattering of crossed molecular beams for the determinntion of information on intermolecular forces and chemical reaction cross sections. A high resolution molecular beam apparatus was constructed to study the interaction of a monoenergetic beam of potassium atoms with a crossed beam of bromine molecules. The device incorporates resistance heated ovens, a helical mechanical velocity selector, and a differential surface ionization detector which distinguishes between potassium and potassium bromide. The construction and performance of this apparatus are discussed in detail. Preliminary experiments with beams of potassium and potassium bromide yielded ionization efficiency vs detector filament temperature curves for the two detector wires (tungsten and 92% platinum --8% tungsten wires) and confirmed the observation that potassium can be distinguished from potassium bromide with such a detector. By varying the speed of rotation of the mechanical velocity selector the velocity distribution of potassium atoms effusing from the oven could be measured. The results agree with theoretical results predicted on the basis of effusive flow and a MaxwellBoltzmann velocity distribution in the oven. During the course of the experiments it was observed that the shape of a wide (0.020 in.) potassium beam profile depended on the speed of rotation of the velocity selector. It was also observed that small intensity satellite peak appeared around the main potassium peak. These two effects were shown to be caused by the geometry of the apparatus. Total collision cross sections for potassium plus bromine as a function of the potassium velocity were determined for potassium beams with velocities in the range from 2.2 x 10/sup 4/ cm/sec to 14.3 x 10/sup 4/ cm/sec. The experimental value of the total collision cross section is about one third the value calculated with the theory of Massey and Mohr, which assumes that scattering is due only to Londan dispersion forces. For example, the measured total collision cross section for potassium (velocity = 6.3 x 10/sup 4/ cm/sec) plus bromine (T = 215 deg K) is 263 x 10/sup -16/ cm/sup 2/ and the calculated total cross section is 832 x 10/sup -16/ cm/sub 2/. A part of the discrepancy may be due to a possible error in the estimation of the effective bromine concentration at the scattering region. The variation of the total collision cross section with relative velocity agrees within the experimental scatter with the predicted variation assuming an attractive poten, tial resulting from London dispersion forces. A number of experiments were performed to ascertain whether any potassium bromide was formed as a result of collisions between potassium and bromine. No potassium bromide could be detected above the background noise level of about 2 to 5 x 10/sup -14/ ampere (on the 0.002 in. diameter detector wire) over the whole range of angles. The maximum flux of an unvelocity selected beam of potassium atoms at the scattering region was about 2 x 10/sup 12/ molecules/cm/ sup 2//sec, and the effective bromine concentration at the scattering region was about 1.4 x 10/sup 12/ molecules/cm/sup 3/. (Dissertation Abstr., 23: No. 5, Nov. 1962)
- Research Organization:
- Originating Research Org. not identified
- NSA Number:
- NSA-17-009141
- OSTI ID:
- 4729932
- Resource Relation:
- Other Information: Thesis. Orig. Receipt Date: 31-DEC-63
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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Related Subjects
ANGULAR DISTRIBUTION
ATOMS
BACKGROUND
BEAMS
BINDING ENERGY
BOLTZMANN STATISTICS
BROMINE
CHEMICAL REACTIONS
CONFIGURATION
CROSS SECTIONS
CURRENTS
DIFFRACTION
DIPOLES
DISTRIBUTION
EFFICIENCY
ERRORS
HEATING
INTERACTIONS
IONIZATION
LONDON FORCES
MASSEY-MOHR EQUATION
MASSEY-MOHR THEORY
MEASURED VALUES
MOLECULES
PERFORMANCE
PLANNING
PLATINUM
POTASSIUM
POTASSIUM BROMIDES
QUANTITY RATIO
RADIATION DETECTORS
RESOLUTION
ROTATION
SCATTERING
SPECTRA
SURFACES
TEMPERATURE
TUNGSTEN
VARIATIONS
VELOCITY
WIRES