Journal of Physical Chemistry A, Vol.112, No.37, 8479-8486, 2008
Investigations of silicon-nitrogen hydrides from reaction of nitrogen atoms with silane: Experiments and calculations
Using a quadrupole mass filter and vacuum-ultraviolet ionization, we measured the time-of-flight spectra of species at mass-to-charge ratios of m/z = 45-42 from the reaction of N + SiH4 in crossed molecular beams. Species with m/z = 44 and 43 correspond to reaction products HSiNH/SiNH2 and HSiN/HNSi, respectively; species with m/z = 45 and 42 are assigned to isotopic variants and daughter ions, respectively, of those two reaction products. We measured the photoionization yields and branching ratios for dissociative ionization of reaction products as a function of photoionization energy. The ionization thresholds of products HSiNH/SiNH2 and HSiN/HNSi were determined to be 6.7 and 9.2 eV, respectively. Furthermore, we calculated the equilibrium structures, electronic energies, and vibrational wavenumbers of various silicon-nitrogen hydrides HxSiNHy (x + y = 0-3) using quantum-chemical methods. SiNH2 ((XB2)-B-2) and HNSi (X-1 Sigma(+)) are more stable than HSiNH (X(2)A') and HSiN ((XE+)-E-1) by 0.82 and 2.81 eV, respectively. SiNH2 (X-2 B-2), HSiNH (X(2)A'), HNSi (X'Sigma(+)), and HSiN (X-1 Sigma(+)) have adiabatic ionization energies of 6.81, 8.19, 10.21, and 10.23 eV, respectively. These experimental and calculated results indicate that SiNH2 ((XB2)-B-2) and HNSi ((XE+)-E-1) are dominant among isomeric products in the reaction of N + SiH4. This work presents the first observation of products from the reaction of N + SiH4 in crossed beams and extensive calculations on pertinent silicon-nitrogen hydrides.