The photoionization spectra of effusive and supersonic molecular beams of monosilane

Abstract

Effusive and supersonic molecular beams of monosilane have been ionized by photons from the Berlin synchrotron light source (BESSY). Photoionization efficiency curves have been taken as a function of wavelength (50 to 120 nm) for a number of fragment ions. The main products observed are SiH+3 and SiH+2 . No appreciable SiH+4 could be detected and less than 5% of the signal was due to lower fragments (SiH+, Si+). The threshold energies Ethr, the standard enthalpy of formation ΔH○f,g of the fragment ions SiH+2 and SiH+3 and the ionization potentials Iz of the corresponding radicals have been determined to be SiH+2: Ethr=11.67±0.04 eV ΔH○f,g=276.3±0.9 kcal/mol, Iz(SiH2)=9.47±0.03 eV. SiH+3: Ethr=12.23±0.02 eV, ΔHf,g=237.1±0.6 kcal/mol, Iz(SiH3)=8.32±0.07 eV. Discrete structure in the photoionization curves is observed in the range of Ethr=15.8–17.6 eV and interpreted as vibrational progressions of a highly excited autoionizing state of SiH4 which lies 15.8 eV above the ground state. Vibrational constants have been found to be 1790±80 and 680±50 cm−1 which correspond to the ground state constants 2187 and 711 cm−1 of the ν1 and the ν2 modes of monosilane. The broadening of some lines in the progression is interpreted as being caused by a transition into a dissociative excited neutral state with lifetimes as short as 3×10−14 s for v=3 of the ν2 mode. Additional ions (predominantly Si2H+4, Si2H+6, Si2H+7) have been observed when photoionizing a supersonic molecular beam of monosilane. These are shown to stem from the ionization and subsequent fragmentation of dimers and possibly higher multimeres. Threshold values have been determined to be Si2H+4: 11.58±0.02 eV; Si2H+6: 11.4 eV; and Si2H+7: 11.4 eV.

Conformational studies on 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane diacetate and 2,2'-oxydi-N-carbethoxycarbazole

“…CH2-0-CH2 bonds are typical of polyoxides like polyethylene oxide), and gauche states about these bonds have an energy 0.9 kcal mol-1 above that of the alternative trans states.18 However, the energy of gauche states about CH2-0 bonds of the carbethoxycarbazole residue was assumed to be 0.3 kcal mol-1 above that of the corresponding trans states, as has been reported for these bonds in polyesters. 18 Second-order interactions CH2-0 and CO"0 were assumed to have energies £ and £ < of 0.6 and 2.1 kcal mol-1, respectively.…”

Photoionization studies of internally reactive small clusters: van der Waals complexes of 1,3-butadiene with sulfur dioxide

“…The threshold region of the photoionization efficiency function for the ionization of the heterodimer, 1,3-C4H6.S02 + hv -(C4H6-S02)+ + e (3) measured at a nozzle pressure of 500 Torr, is displayed in Figure 6. The onset occurs at 9.062 ± 0.020 eV (1368 ± 3 Á) with no evidence of a still lower onset.…”

Intracluster Ion−Molecule Reactions of Dimer Cations of Phenylsilanes

“…This fact can be interpreted based on the above mechanism 2. Since the heat of formation of (145.8 kcal/mol) is much smaller compared with that of SiH 3 (237 kcal/mol), it is expected that the exothermicity of the + C 12 H 13 Si channel 3a is larger than that of the C 15 H 19 Si + + SiH 3 channel 10. This is the reason of the occurrence of the + C 12 H 13 Si channel.…”