Photoionization experiments using light from the Berlin synchrotron facility BESSY were performed with methane clusters. A number of ionic reaction products with masses m = k + 16n (k = 16, 17, 28, 29, 31, 40, and 57 and n> 0) were determined. These are interpreted as series of cluster ions of the form [X-(CH4)"]+ with X = CH4, CH5, C2H4, C2H5, C2H7, Ar, and Ar-CH5. For all series except two (X = C2H4, C2H7) analogue ion-molecule reactions in the gas phase were observed. The occurrence of these two exceptions is believed to be caused by the cluster environment which contains the reagents for a much longer time than that observed in gas-phase reactions. Some of the reactions (X = CHS, C2H5, Ar, Ar-CH5) exhibit Ar interband transitions, which are believed to originate from neutral precursor clusters with an abundance of Ar atoms.Possible reaction schemes are discussed and compared with the analogue ion-molecule reactions in the gas phase.

A drift tube-mass spectrometer system employing Bradbury-Nielsen shutters has been used to measure the mobility of Li + ions in He at 294 and 80 K and Li + ions in Ar at 294 K. The E/N range used was 3 to 80 Td (1 Td == 10 -21 Y cm 2 ). The zero field reduced mobility for Li + in He was found to be 22·81±0·11 cm 2 y-1 s-I at 294 K and 19·64±0·29 cm 2 y-1 s-I at 80 K. The value for Li+ in Ar at 294 K is 4·66±0·22 cm 2 y-1 s-I. The reduced zero field mobility for the cluster ion Li +. He in He at 80 K and low values of E/ N was found to be 14·84 ± 0·22 cm 2 y -I s -I. The equilibrium constant for the formation and dissociation of Li + . Ar cluster ions at 294 K was obtained by fitting to the variation of the measured mobility with gas number density at low E/N values. The value obtained, corresponding to thermal equilibrium at 294 K, was (4±0.5)xlO-19 cm 3 .

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.

Abstract'A drift tube-mass spectrometer has been used to measure the mobility of K + ions in helium at 294 and 80 K over the EIN range 5-60 Td and in argon at 295 K over the EIN range 3-120 Td. The zero field reduced mobility KO for K + in He was determined to be 21· 14 ± 0 . 11 cm 2 Y -1 s -1 at 294 K and 17 ·32±0·26 cm 2 y-1 s-l at 80 K. The value of KO obtained for K+ in Ar at 295 K is 2 ·640±0·013 cm 2 y-1 s -1. The results are compared with those obtained in previous measurements.

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