Photoionization mass spectrometric studies of SiH n ( n =1–4)

105

Electron-impact total ionization cross sections of some silicon and germanium compounds have been calculated by applying a new theoretical model that has been found to be reliable for a wide range of molecules. The new theory, the binary-encounter-Bethe (BEB) model, combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses simple theoretical molecular orbital data-binding energies, average kinetic energies, and occupation numbers-which are readily available from molecular structure codes. Total ionization cross sections of SiH, SiH 2 , SiH 3 , SiH 4 , Si 2 H 6 , Si(CH 3 ) 4 , GeH, GeH 2 , GeH 3 , GeH 4 , and Ge 2 H 6 are presented for incident electron energies T from threshold to 1 keV, and compared to available experimental data. Theory and experiment agree well for SiH x , x=1-4, from thresholds to T<80 eV, while theoretical peaks occur at lower T than experimental peaks for SiH x , x=1-3. No experimental data are available for germanium hydrides for comparison. The theoretical cross sections are given by a compact analytic form suitable for applications in plasma processing. ©1997 American Institute of Physics. History:Received 27 January 1997; accepted 4 March 1997 Electron-impact total ionization cross sections of some silicon and germanium compounds have been calculated by applying a new theoretical model that has been found to be reliable for a wide range of molecules. The new theory, the binary-encounter-Bethe ͑BEB͒ model, combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses simple theoretical molecular orbital data-binding energies, average kinetic energies, and occupation numbers-which are readily available from molecular structure codes. Total ionization cross sections of SiH, SiH 2 , SiH 3 , SiH 4 , Si 2 H 6 , Si͑CH 3 ͒ 4 , GeH, GeH 2 , GeH 3 , GeH 4 , and Ge 2 H 6 are presented for incident electron energies T from threshold to 1 keV, and compared to available experimental data. Theory and experiment agree well for SiH x , xϭ1 -4, from thresholds to T Ͻ80 eV, while theoretical peaks occur at lower T than experimental peaks for SiH x , xϭ1 -3. No experimental data are available for germanium hydrides for comparison. The theoretical cross sections are given by a compact analytic form suitable for applications in plasma processing.

Section: Discussionmentioning

confidence: 87%

Section: Application To Moleculesmentioning

confidence: 99%

Electron-impact total ionization cross sections of silicon and germanium hydrides

Ali

Kim

Hwang

et al. 1997

105

“…Work on these two states includes the determination of ⌳-doubling transition frequencies for X 2 ⌸, 38,63,65,76 radiative lifetimes and oscillator strengths of the A 2 ⌬ϪX 2 ⌸ system, 43,45,47,61,64,74 various molecular constants, 55,56,67,72,78,79,84 transition moments, 66 ionization potentials, 55,80,81 and dissociation energies and enthalpies of formation. 55,59,64,68,80,81,83 To our knowledge, only a limited number of experimental papers deal with the higher excited states, but the extracted parameters useful to the present theoretical work are very few, limited mostly to term values. These papers include the work of Verma, 55 Herzberg et al, 60 Bollmark et al, 62 and Johnson and Hudgens.…”

Section: Introductionmentioning

confidence: 99%

An accurate description of the ground and excited states of SiH

Καλέμος

Mavridis

Metropoulos

2002

The astrophysical importance of the SiH radical has motivated significant experimental and theoretical work. However, only the X 2 ⌸ and A 2 ⌬ states of SiH have been extensively investigated experimentally, while the study of higher excited states is rather limited. From a theoretical point of view, most of the studies have been focused on spectroscopic and thermochemical quantities of the ground state. The lack of accurate spectroscopic parameters (r e ,D e , e , e x e ,␣ e ,D e ,T e ) pertaining to higher excited states was the driving force of the present work, in line with our previous study of the isovalent CH molecule ͓A. Kalemos, A. Mavridis, and A. Metropoulos, J. Chem. Phys. 111, 9536 ͑1999͔͒. Using the multireference configuration interaction approach coupled with very large correlation-consistent basis sets, we have constructed potential energy curves for 18 molecular states correlating to Si( 3 P,At the same level, the potential energy curve of the ground SiH ϩ state (X 1 ⌺ ϩ ) has also been constructed. We report total energies, dissociation energies, and the usual spectroscopic constants for 28 2 H and for all states studied. Most of our results are in excellent agreement with existing experimental values. In particular, we believe that our dissociation energy for the X state, D e ϭ73.28 kcal/mol, is the most reliable reported so far in the literature.

“…However, there are only a few experimental data for the singlet-triplet energy gaps of the fluorine-substituted methylenes and silylenes. [4][5][6][7] Current knowledge about I:J.Esr for these systems is as follows.…”

Section: Introductionmentioning

confidence: 99%

Singlet–triplet energy gaps in fluorine-substituted methylenes and silylenes

Shin

Goddard

Beauchamp

1990

We report singlet and triplet state splittings (I:J.EsT) for fluorine-substituted methylenes and silylenes using dissociation-consistent configuration interaction (CI) (based on generalized valence bond wave functions). These relatively simple CI calculations emphasize correlation consistency between the singlet and triplet states. Values of I:J.Esr for CH 2 , CF 2 , SiH 2 , and SiF 2 are in excellent agreement with available experimental results, and we expect the predictions for the other cases CHF (14.5) and SiHF ( 41.3) to be equally accurate. This result strongly suggests that the correct choice among the experimental values for I:J.Esr of CHF is 14.7 ±0.2 kcal/mol.