The vaporization behavior of the systems boron—carbon and boron—carbon—silicon has been studied with a mass spectrometer. In addition to the gaseous species characteristic of graphite, silicon carbide and boron, the molecules BC2, B2C, BCSi, BSi2, BC, and BSi were identified and their atomization energies measured. The values are: 294, 254, 247, 174, 106, and 68 kcal/mole, respectively. The atomization energies of SiC, Si2C, and SiC2 have been redetermined.

The evaporation of tin oxide SnO2 and mixtures of tin and tin oxide was studied. The vaporization reactions are 1 1SnOz(s) *$sno),(g) + 5 0 2 9 (n = 1, 21, 1 1 1 -Sn(s,l)+zSnO~(s) -.;;(SnO),,(n = 1,2,3,4.) 2The dissociation energy of the molecule SnO was determined : Dg = 126.5+2.0 kcal/mole ; as well as the polymerization energies = 66.814, 136.515, 207.6f5 kcal/mole for (Sn0)2, (Sn0)S snd (SnO)4 respectively. A re-interpretation of the total vapour pressures given in the literature was made. The presence of the polymeric molecules is the cause of previously unexplained differences.* The research reported in this document has been sponsored in part by Air Force Materials Laboratory, Research and Technology Division, AFSC under Contracts AF 61 (052)-225 and -764 through the European O f f i c e of Aerospace Research (OAR), United States Air Force.

The equilibrium vapor effusing from a Knudsen cell, in which solid ND.CI was evaporated, was analyzed by a quadrupole mass spectrometer. In the temperature range considered (335°-485°K) the main vaporization process corresponds to the decomposition of the solid towards gaseous NDa and DCI; the measured enthalpy change llHo'07 d •• [ND.CJ(s)]=42.6±2.0 kcal mole-I is very close to that measured for NILCI: llHo'07 d .. [NILCI(s)]=42.5 kcal mole-I. Apart from the main gaseous species, small proportions (5X1o-L 2X1o-3 ) of ND.CI molecules were also observed. The ND.CI molecule fragments (>99%) under electron impact and yields the ND.+(m/e=22) ion. From the observed ion intensity ratios, as well as their dependence on temperature, DoO(NILCI~NHa+HCI) = 10.0±3.0 kcal mole-I was obtained confirming Clementi's computed prediction <14.0 kcal mole-I.

Results of calculations using a configuration interaction LCAO-MO method are presented for the X 2Σ+ and A 2Π states of BeH. Apart from the 1s shell of Be, the correlation energy of the remaining three electrons is calculated quantitatively using an extended basis set and complete configuration interaction including all single, double and triple replacements. The calculated spectroscopic constants are in excellent agreement with available experimental data. The present calculations also predict a value of De(BeH, X 3Σ+)=2.115 eV, and dismiss the possibility of a potential maximum in the ground state potential energy curve.

Ab initio calculations (LCAO–MO–SCF) are performed on a series of valence levels of the molecules CH and NH+. Correlation energies are estimated semiempirically from corresponding atomic data. Close agreement with experiment is found for known states for a series of molecular properties such as equilibrium internuclear distances, vibration frequencies, term values, and dissociation energies. A low-lying Σ4− state in CH is calculated to lie 7500 cm−1 above the X 2Π state. No observable quartet transition could be found for CH, while for NH+ a Π4−Σ4− transition should occur in the region of 1000 Å. Other qualitative differences in the observed spectra of the two molecules are discussed. Finally a value of D00(NH+) = 3.4 eV is calculated.