Georges Verhaegen

Mass Spectrometric Study of the Systems Boron—Carbon and Boron—Carbon—Silicon

Abstract : The systems B-C and B-C-Si were investigated mass-spectrometrically. The atomization energy of the newly identified molecules BC2, B2C, BCSi, BSi2, BC and BSi are 294, 254, 247, 174, 107 and 68 kcal/mole respectively. The atomization energy of SiC2, Si2C and SiC was redetermined.

Electronic States of CH and NH

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 4Σ− 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 4Π–4Σ− transition should occur in the region of 1000 A. Other qualitative differences in the observed spectra of the two molecules are discussed. Finally a value of D00(NH+) = 3.4 eV is calculated.

Stability of the Gaseous Ammonium Chloride Molecule

The equilibrium vapor effusing from a Knudsen cell, in which solid ND4Cl 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 ND3 and DCl; the measured enthalpy change ΔH°407dec[ND4Cl(s)] = 42.6 ± 2.0 kcal mole−1 is very close to that measured for NH4Cl: ΔH°407dec[NH4Cl(s)] = 42.5 kcal mole−1. Apart from the main gaseous species, small proportions (5 × 10−5–2 × 10−3) of ND4Cl molecules were also observed. The ND4Cl molecule fragments (> 99%) under electron impact and yields the ND4+(m / e = 22) ion. From the observed ion intensity ratios, as well as their dependence on temperature, D0°(NH4Cl ⇋ NH3 + HCl) = 10.0 ± 3.0 kcal mole−1 was obtained confirming Clementis computed prediction < 14.0 kcal mole−1.

Accurate ab initio calculation of the BeH molecule. I. The X 2Σ+ and A 2Π states

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.

Theoretical Calculation of the Electronic States of C2

Results of ab initio calculations are presented for a series of valence levels of C2+ and for the two lowest states of C2 (x 1Σg+and X′ 3Πu). Correlation energies of all the levels are estimated by a new scheme taking into account near‐degeneracy effects in the molecule and in the constituent ion pairs. Results for C2 are in close agreement with experiment for equilibrium internuclear distances, vibration frequencies, term energies and dissociation energies. For C2+ the calculations show the ground state to be 4Σg− with relatively low‐lying (∼ 0.6 eV) 2Δg and 2Πu levels. The electron‐impact measurement for the appearance potential of C2+ is interpreted as C2(3Πu, υ = 1) → C2+(4Σg−, υ = 0). The quartet transition 4Σg− → 4Σu− is predicted to lie at 6000 A. The major doublet transitions all lie in the infrared.

Mass Spectrometric Study of the Gaseous Molecules above AgSn, AuSn, and CuSn Alloys

Mass spectrometric technique has been employed to analyze the molecular beams effusing from mullite Knudsen cells containing Sn and alloys of Cu, Ag, and Au with Sn. From the experimental intensities of monatomic and diatomic species and the vapor pressure of Sn, the following dissociation energies are obtained: D0∘(Sn2)=45.8±4 kcal/mole,D0∘(AgSn)=31.6±5 kcal/mole,D0∘(AuSn)=57.5±4 kcal/mole,D0∘(CuSn)=41.4±4 kcal/mole.

Mass spectrometric determination of the dissociation energy of the molecules MgO, CaO, SrO and Sr2O

Abstract : The diatomic molecules Sc2, Y2, La2 and YLa have been identified mass spectrometrically in the vapors above condensed scandium, yttrium, lanthanum and Y-La alloys respectively. Their dissociation energies are Sc2 25.9 = 5, Y2 37.3 = 5, La2 57.6 = 5 and YLa 47.3 =5 kcal/mole.

Relativistic energies of excited states of atoms and ions of the second period

Relativistic energies are computed for a series of j states corresponding to 1s22sm2pn (0?m?2; 0?n?6) configurations by solution of the hartree-fock-dirac equations. The j states calculated are those states whose eigenfunctions within a configuration correspond to a unique and maximum eigenvalue of the operator j2. In addition, average relativistic energies are obtained for all configurations considered. The two sets of results are compared, and in certain cases (for the 1s22p, 1s22p5, 1s22s22p, 1s22s22p5 configurations) permit a determination of multiplet splittings (e(2p12/-2p32/)). The results of these splittings are in excellent agreement with available experimental data. The present results also tend to confirm the assumption that the relativistic energy contributions for the j averaged ls states are the same for all states arising from the same configuration. This makes it possible to evaluate the relativistic energies of all states belonging to the configurations of interest to this paper. These in turn serve to re-evaluate more correctly recently obtained correlation energies for the same states.

A correlation energy calculation of the 1s hole state in neon

Abstract The Bethe-Goldstone formalism for calculating correlation energy has been applied to the 1s hole state in neon. The binding energy of the 1s electron is computed to be 870.0 eV which is in excellent agreement with experiment.

Ab initio study of the O4 molecule

Abstract SCF-CI calculations were done on tetratomic oxygen complexes at various geometries. The results point to the existence of a metastable covalent molecule O 4 completely different from the van der Waals structure (O 2 ) 2 detected experimentally. At its equilibrium geometry, the O 4 molecule is a quasi-square ( r (OO) ≈ 1.4 A), slightly twisted out of plane, corresponding to the symmetry group D 2d . The activation energy of the reaction O 4 ( 1 A g ) → 20 2 (X 3 Σ − g ) is found to be ≈ 15 kcal/mole, that of the inverse reaction, ≈ 75 kcal/mole.