Austin L. Wahrhaftig

Mass Spectrum of Propane: Isotope Effect and Metastable Ions

The mass spectra of propane and of propane‐2,2‐d2 have been calculated assuming that the mass spectra result from successive and competing unimolecular reactions following initial vertical ionization of the parent molecules. Reasonable agreement with experiment is found for the change in mass spectral pattern with deuterium substitution. The metastable ion peaks are shown to be a normal part of the mass spectrum.

DEPENDENCE OF CALCULATED AND EXPERIMENTAL PROPANE MASS SPECTRA UPON ELECTRON VOLTAGE

Experimental propane mass spectra have been obtained with bombarding electrons ranging in energy from 14 to 500 v. The quasi‐equilibrium theory has been used in calculating the same spectra. The grossly simplified version of the statistical theory that satisfactorily predicts the 70‐v mass spectrum is inadequate at low voltages, but if half the theoretical number of oscillators are assumed to be effective in the parent‐ion and activation energies that bear no simple relation to experimental appearance potentials are employed, a semiquantitative fit of the experimental data is obtained. The description of the decomposition reaction of a molecule‐ion in terms of a collection of harmonic oscillators is clearly unsatisfactory. However, the more general form of the quasi‐equilibrium theory, in which it is assumed only that the reaction coordinate is separable, does appear to be applicable.

Problems in the gas phase isolation of nonvolatile molecules by high pressure jets for mass spectrometry

Abstract The possibility that nonvolatile molecules can be isolated in the gas phase through a rapid decompression of their solution in a compressed gas solvent at pressures of the order of 10 3 atmospheres is examined. Crucial to this process are (a) the existence of sufficient internal energy to break up the solute—solvent cluster, (b) rates of dissociation great enough to give complete dissociation of solvent and solute and (c) a limited degree of association between solute molecules. Each of these conditions is examined theoretically with assumed parameters to represent typical macromolecules. The treatment suggests that condition (c) is most stringent, requiring extremely rapid decompression in order to avoid undue solute loss. Nozzles for decompression from 1000 to 1 atm have been constructed, using Nichrome V foil with laser-drilled holes of diameter from 5 to 25 μm. The flow properties have been characterized. The resulting jet successfully transports β-carotene to the low pressure side. Mass spectral studies of a solution of squalane in argon indicated that the squalane is localized in the jet but further studies with a complete jet-skimmer system are required to establish the overall feasibility of the method.

Consecutive Metastable Peaks in Mass Spectra

The observation of consecutive metastable peaks in mass spectra has prompted a calculation for the abundance of these species. Expressions for fractional abundance as a function of primary and secondary rates and residence times are derived for all species of normal and metastable ions. Primary and secondary rates for a toluene consecutive dissociation were calculated using the method of Vestal, Wahrhaftig, and Johnston, and the breakdown curves were determined. By assuming a constant energy‐transfer function the normalized areas of the calculated curves are found to compare very favorably with the mass spectrum obtained in this laboratory with a double‐focusing mass spectrometer.

Rotational analysis of the à 2E1/2(0,1,7)←X̃ 2E1/2 (0,0,0) transition in CH3I+

A computer simulation of the partially resolved rotational structure observed in the photodissociation spectrum of methyl iodide ion was undertaken in an attempt to determine the extent of rovibronic interaction in this polyatomic ion. From a series of calculations a set of rotational constants have been derived which give a simulated spectrum strongly resembling that obtained experimentally for the A 2E1/2(0,1,7)←X 2E1/2(0,0,0) band of CH3I+. The series of prominent peaks observed in the experimental spectrum are reproduced in the simulated spectrum and are due to P branch progressions, within the q subbands, which nearly coincide in energy. The corresponding R branch ‘‘lines’’ are weak by comparison and are lost in the surrounding unresolved rotational lines. The encouraging fit obtained when Hund’s case (c) coupling is assumed for the A state is indicative of strong spin‐orbit coupling in the A state, caused by interaction between the A and B states of the ion. The rotational constants obtained f...