Characterization of Si atomic transitions using pulsed electric discharge and resonance-enhanced multiphoton ionization techniques
Atomic Si was produced in a pulsed high-voltage discharge jet expansion of a gaseous mixture of tetramethylsilane in helium. Its atomic transitions were characterized by a single color (1 + 1) resonance-enhanced multiphoton ionization (REMPI) technique in the one-photon energy range of 38 466–46 075 cm−1. Based on the mass analysis of the discharge species using vacuum ultraviolet laser single-photon ionization time-of-flight mass spectrometry, which provides a means to characterize the species produced by the discharge source, various species including atomic Si, silicon hydrides (SiHa, a = 0–3), hydrogenated silicon carbides (SixCyHz), and hydrocarbon species (CmHn) were generated in the pulsed high-voltage discharge jet expansion of tetramethylsilane. The REMPI spectroscopic characterization of the mass-selected species with 28 amu showed a total of 26 lines, all of which were assigned to the electronic transitions of neutral Si atoms. 10 out of the 26 lines were from spin-forbidden transitions. Among them are two “new” lines that were not listed in the M.I.T. Wavelength Tables or NIST Atomic Spectra Database. They were observed with good signal intensity at 43 551.76 cm−1 (XVIII) and 44 201.34 cm−1 (XX) and assigned to 3s23p3d[3F02] ← 3s23p2[1D2] and 3s23p3d[3P02] ← 3s23p2[1D2] transitions, respectively. In addition, 3 lines observed at 38 790.14 cm−1 (I), 41 306.00 cm−1 (XVI), and 43 634.78 cm−1 (XIX), that had been previously reported in the literature, but with no assignment, were assigned to the spin-forbidden transitions of 3s23p3d[3D01] ← 3s23p2[1S0], 3s23p4d[3P01] ← 3s23p2[1S0] and 3s23p3d[3F03] ← 3s23p2[1D2], respectively. The use of a pulsed high-voltage electric discharge jet coupled with mass-selective REMPI has been shown as a sensitive and powerful technique to generate a rich variety of atomic and molecular species and to probe their electronic transitions with increased sensitivity.