A mass spectrometric method for the determination of dissociation energies of diatomic molecules

By combining experimental data obtained in a mass spectrometer with thermochemical computations, dissociation energies of various diatomic molecules have been determined. This method has been applied to the Group IB and IVB dimers, and estimates have yielded values for Group IIIB and some other elements. To produce atomic and diatomic species ot a given element, a milligram sample was vaporized in a mass spectrometer from a small, electrically-heated crucible. Ion intensity ratios were measured as a function of temperature, after the particles had been ionized, accelerated, mass analyzed and collected The dissociation energies computed by the Absolute Entropy Method are based on the following quantities: ion intensity ratios: internuclear distances, estimated from known crystal spacings; electronic partition functions; and vibrational frequencies reported recently in band spectral studies. The values found agree well with those obtained by the so-called Slope Method which utilizes directly the measured heats of vaporization of monomers and duners, and they fall within the upper limits set by band spectral data.SCOPUS: ar.j