Bilin P. Tsai

Multiphoton ionization of SiH3 and SiD3 radicals: Electronic spectra, vibrational analyses of the ground and Rydberg states, and ionization potentials

The electronic spectra of silyl radicals, SiH3 and SiD3, were observed between 310 and 430 nm (46 000–64 000 cm−1) by resonance enhanced multiphoton ionization (REMPI) mass spectroscopy. The spectra were generated through a 2+1 REMPI mechanism. Two Rydberg series originating from planar, D3h point group states were observed. One series, of quantum defect δ=1.45(2), is comprised of the E 2A‘2(4p), J 2A‘2(5p), and M 2A‘2(6p) Rydberg states which have origins at ν0–0 =48 438, 56 929, and 60 341 cm−1 in SiH3 and at ν0–0 =48 391, 56 874, and 60 267 cm−1 in SiD3. In SiD3 theP 2A‘2(7p) Rydberg origin was observed at ν0–0 =62 002 cm−1. The H, K, and N states observed in the SiD3 spectrum comprise the second Rydberg series, δ=2.09, and were tentatively assigned as ns 2A’1 Rydberg states (n=5, 6, 7). The K and N origins were observed at ν0–0 =58 417 and 61 005 cm−1. A fit of the Rydberg formula to the np 2A‘2(n≥5) origins found the adiabatic ionization potential of the SiH3 and SiD3 radicals to be IPa=8.13...

The electronic spectrum of the GeH3 radical

The germyl (GeH3) radical has been observed by resonance enhanced multiphoton ionization (REMPI) spectroscopy in the region of 370–430 nm. The spectrum arises from two‐photon resonances with the 5p 2A‘2 (D3h) Rydberg state that possesses an origin at 419.1 nm (ν0–0 =47 705 cm−1). A vibrational progression of 756 cm−1 was assigned to the ‘‘umbrella’’ mode, ν2. The observed X 2A1 (C3v) v‘2=2 to v‘2=0 vibrational interval is 663 cm−1 which leads to an estimated barrier to inversion of 1530 cm−1.

Resonance enhanced multiphoton ionization spectra of the GeF and GeCl radicals from 400 to 500 nm

The resonance enhanced multiphoton ionization spectra from 400 to 500 nm of the GeF and GeCl radicals are reported. In GeF bands involving transitions to the A 2Σ+, C’ 2Π, D’ 2Π, E 2Σ+, and G 2Δ states were observed. The bands involving transitions to the valence A 2Σ+ state were accounted for by 1+2 and 1+1+1 resonance enhanced multiphoton ionization (REMPI) mechanisms. Bands associated with the other Rydberg states were generated by a 2+1 REMPI mechanism. The spectrum of the GeCl radical arose from 2+1 REMPI excitation through the C’ 2Πr (5pπ) and C 2Πr (4pπ) Rydberg states. The C’ 2Πr state spin–orbit coupling constant was determined by direct measurement of C’ 2Π1/2←←X 2Π1/2 transitions and ‘‘one photon forbidden’’ C’ 2Π3/2←←X 2Π1/2 transitions. A least‐squares fit determined the spectroscopic constants of the C’ 2Πr 5pπ Rydberg state of GeCl: Te=42 190±5 cm−1, Ae=81.0±3.5 cm−1, ωe=509.2±5.3 cm−1, and ωexe=3.3±1.1 cm−1.

New electronic spectra of the CHFCl radical observed with resonance enhanced multiphoton ionization

The structures and optical spectroscopy of the CHFCl radical and cation were studied by ab initio molecular orbital calculations and by experiment. Ab initio calculations at the MP2/ 6–311++G** theory level found that the optimum structure of the CHFCl+ (X 1A’) cation is planar with r(C–H)=1.092 A, r(C–F)=1.254 A, r(C–Cl)=1.599 A, ∠H–C–F=116.85°, and ∠H–C–Cl=122.14°. CHFCl (X 2A’) radical is nonplanar with r(C–H)=1.083 A, r(C–F)=1.335 A, r(C–Cl)=1.705 A, ∠H–C–F=113.49°, ∠H–C–Cl=116.68°, and ∠F–C–Cl=114.44°. The ab initio angle between the F–C–Cl plane and the C–H bond is Φe=38° and the inversion barrier is Binv=1190 cm−1. Using isogyric reactions to obtain empirical corrections, we calculate IPa(CHFCl)=8.37±0.05 eV. Ab initio vibrational frequencies are reported. The electronic spectrum of the CHFCl radicals was observed between 340–420 nm using one color, mass resolved, 2+1 resonance enhanced multiphoton ionization (REMPI) spectroscopy. The spectrum arises from two‐photon resonances with the planar F(...

Spectrum (310 to 360 nm) and ionization potential of the silyl radical

The spectra of the silyl radical (SiH3) and its perdeuterated analogue (SiD3) have been observed by resonance enhanced multiphoton ionization spectroscopy. The spectra arise from two‐photon excitation to the 5p, 6p and 7p Rydberg states. In the SiH3 5p state a vibrational progression of the symmetric deformation mode ν2 with spacings of ∼825 cm−1 are observed. The vibrational spacings are 600–620 cm−1 for SiD3. The observation of several Rydberg states allows a determination of the ionization potentials. They are 8.128 eV for SiD3 and 8.135 eV for SiH3.

Two Photon Resonance Enhanced Multiphoton Ionization Detection and Spectroscopy of Gas Phase Germyl (GeH3) Radicals

GeH3 radicals were observed by resonance enhanced multiphoton ionization (REMPI) spectroscopy in the region of 370 − 430 nm. The spectrum arises from two‐photon resonances with the 5p 2A″2 (D3h) Rydberg state which has its origin at 419.1 nm (ν0 ‐ 0 = 47,705 cm−1). Absorption of a third photon ionized the radicals. A vibrational progression of ∼756 cm−1 was assigned to the “umbrella” mode, ν′2. The observed X 2A1 (C3v) v″2=2 to v″2=0 vibrational interval is 663 cm−1.