Knudsen bond energy determination

The Knudsen effusion method In conjunction with mass spectrometrlc analysis has been used to determine the bond energies and appearance potentials of diatomic metals and small metallic clusters. The experimental bond energies are reported and Interpreted In terms of various empirical models of bonding, such as the Pauling model of a polar single bond, the empirical valence bond model for certain multiply-bonded dlatomlcs, the atomic cell model, and bond additivity concepts. The stability of positive Ions of metal molecules Is also discussed. 

The most reliable values for the bond energies of the majority of these molecules have been obtained by using Knudsen effusion mass spectrometry ( ). For some of them, notably the alkali dimers, and Group IIA and Group IIB dimers, as well as for some of their intermetallic diatomic molecules, optical spectroscopic methods have provided the best or only determination of dissociation energies ( 3, ). 

Selenium-Oxygen Compounds.—Knudsen effusion measurements have been performed on powdered selenium dioxide at temperatures between 374 and 427 K, and the vapour pressure over this range has been determined.295 The enthalpy of formation of Se02(g) was computed to be AHT(298.i5) — -26.20 kcal mol-1 this leads to a value for an average bond energy of 99.80 kcal moF1, which is comparable with the spectroscopic dissociation energy. A vibrational analysis of the 3130 A absorption system of selenium dioxide has been carried out.296... 

In the field of metals or alloys gaseous complex Zintl compounds were identified for the first time. The combination of the results of all electron ab initio computations and Knudsen effusion mass spectrometry have made the determination of improved values for bond energies possible. Moreover, bond energies for transition metal trimers were obtained for the first time. 

Bonds to Sulphur or Selenium.— Values for the dissociation energies (Do) of the diatomic species PS, PSe, and PTe, determined by Knudsen-cell mass spectrometry, are 438, 360, and 294 kJ mol 1, respectively.583 Some 3lP n.m.r. data for P4S3 in the polycrystalline state584 and in a nematic phase are now available.585 Displacement of one carbon monoxide group from Mo(CO)6 occurs on reaction with P4S3, giving (84),586 and crystal data show... 

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