Masaru Fukushima

Jet spectroscopy and excited state dynamics of benzyl and substituted benzyl radicals

Benzyl and its p‐fluoro and p‐methyl derivatives are produced by the ArF laser (193 nm) photolysis of their chlorides in the supersonic free jet. The spectroscopy and excited state dynamics of these radicals are studied by the laser induced fluorescence (LIF) method under the collision free condition. The assignments of vibronic bands are carried out from the LIF excitation and dispersed spectra and the vibrational energies of the D1 state are determined. The excitation spectrum of p‐fluorobenzyl shows quite similar vibrational structure to that of p‐fluorotoluene up to about 1000 cm−1 from the 000 band, which indicates that D2 of p‐fluorobenzyl lies about 1000 cm−1 above D1 and no vibronic coupling exists lower than this energy. On the other hand, benzyl and p‐methylbenzyl show very complicated and irregular vibronic structures in excitation spectra, which are not similar to those of toluene and p‐xylene. This complication is explained by the D1–D2 vibronic coupling caused by low lying D2 states in these...

Jet spectroscopy and excited state dynamics of SiH2 and SiD2

Silylene radicals, SiH2 and SiD2, are generated in a supersonic free jet by ArF laser (193 nm) photolysis of phenylsilane and phenylsilane‐α‐d3, respectively. LIF excitation and dispersed fluorescence spectra are measured for the ν2 vibronic bands of the Au20091B1−Xu20091A1 transition. The heterogeneous predissociation to Si (3P)+H2 is proposed from the anomalous rotational structure in the excitation spectra; the rotational lines of the r(1) subbranch (K’a=0←K■a=1) have stronger intensity than those of the r(0) subbranch (K’a=1←K■a=0), though the latter is expected to be stronger due to the low temperature Boltzmann distribution in the jet. The time‐resolved excitation spectra demonstrate shorter lifetime of K’a=1 rovibronic levels in the Au20091B1 state.The heterogeneous predissociation is interpreted with the second order perturbation: Au20091B1 –(a‐type Coriolis)→Xu20091A1 ‐(spin–orbit)→au20093B1→Si(3P)+H2. It is demonstrated experimentally that there is a potential barrier associated with the dissociation path of au20093...

Emitting states of benzyl, p-fluorobenzyl and p-cyanobenzylradicals

Abstract Polarization studies of the fluorescence emission and excitation spectra have been carried out by the photoselection method for the benzyl, p -fluorobenzyl and p -cyanobenzyl radicals in poly (vinyl alcohol) films at 77 K. The emitting states have been assigned to the 1 2 A 2 electronic state for the benzyl and p -fluorobenzyl radicals and the 2 2 B 2 state for the p -cyanobenzyl radical. Flu lifetimes have been determined to be 1.22±0.10, 0.36±0.04 and 0.43±0.04 μs for the three radicals, respectively.

Jet spectroscopy of benzyl and benzyl‐α‐d2

Benzyl and benzyl‐α‐d2 radicals are produced by the ArF laser (193 nm) photolysis of benzylchloride and benzylchloride‐α‐d2, respectively, in a supersonic free jet. The spectroscopy of the D1 1u20092A2–D0 1u20092B1 transition of these radicals is studied by means of the laser induced fluorescence (LIF) method. LIF excitation spectra show well resolved but unusual vibrational structure. The assignments of vibronic bands have been carried out on the basis of dispersed spectra from the single vibronic level (SVL) and transition band types derived from rotational analysis of high resolution LIF excitation spectra. The intensity anomaly of the vibronic bands in the excitation spectra is interpreted as the breakdown of the accidental forbidden character of the D1–D0 and D2–D0 electronic transitions, whose mechanism will be discussed in terms of vibronic coupling.

Rotational analysis of the SiD2 Ã 1B1–X̃ 1A1 transition observed in a jet

The SiD2 radical was produced by ArF laser photolysis of C6H5SiD3 in a free‐jet expansion, and the laser‐induced fluorescence (LIF) excitation spectrum of the Au20091B1–Xu20091A1 transition of SiD2 was measured. The LIF excitation spectra of the five vibronic bands, (0,v2’,0)–(0,v2‘,0), v2’–v2‘= 0–0, 1–0, 2–0, 1–1, and 2–2, were obtained using a narrow‐band dye laser with an intracavity etalon, the resolution of which attained to ∼0.03 cm−1. The rotational structures of the vibronic bands were well analyzed by a Hamiltonian including fourth‐order terms, and the molecular constants were determined for the vibronic levels, v2=0, 1, and 2, of the Au20091B1 and Xu20091A1 states. By comparing the observed rotational line intensities with simulated ones, we found two kinds of intensity anomalies depending on the rotational quantum numbers J and Ka. We conclude that both the anomalies are caused by a predissociation process to the dissociation continuum, Si(3P)+D2, which was proposed in our previous paper [J. Chem Phys. 96,...

Spectroscopy and kinetics of thiophenoxy radicals in the gas phase

Abstract Thiophenoxy radicals C 6 H 5 S in the gas phase have been studied by LIF following the 248 nm photolysis of thiophenol or thioanisole. The absorption bands between 490 and 520 nm are assigned to an electronic transition of thiophenoxy radicals with its origin at 19328±4 cm −1 . Vibrational progressions in absorption and emission are mainly built by the Cue5f8S stretching mode. The fluorescence lifetime was shorter than the time resolution of the system employed (≈ 20 ns). The LIF technique was applied to monitor the time evolution of the thiophenoxy radical in the ground state. The reaction rate constants of the thiophenoxy radical with NO and O 2 at room temperature are determined to be (2.96±0.22) × 10 −11 and (2.52±0.29) × 10 −12 cm 3 molecule −1 s −1 , respectively.

LIF spectroscopy and dissociation dynamics of the SiH2 radical in the Ã1B1 (1,v2, 0) state

Abstract Laser-induced fluorescence (LIF) excitation spectra of the SiH 2 A (1,0,0) – and A (1,1,0)–X (0,0,0) bands, and dispersed fluorescence (DF) spectra from the A (1,0,0) and (1,1,0) levels were measured in the supersonic-free jet. From the rotational structures of the excitation spectra, the rotational constants in A (1, v 2 ,0), v 2 =0∼2, were determined. The fluorescence decay profiles of the single ro-vibronic levels were also measured, and the fluorescence lifetimes were determined. Based on the lifetimes, it was found that the predissociation depending on the vibronic level starts between the A (1,4,0) and (1,5,0) levels, and the predissociation depending on the rotational level in the A state is suppressed by the ν 1 mode excitation and is promoted by the ν 2 mode. The latter one is qualitatively explained by considering a second-order predissociation mechanism and a rotation-vibration constant, α i A .

Detection of silylene and germylene radicals by laser-induced fluorescence

Abstract Silylene and germylene radicals are generated in the supersonic free jet by ArF laser photolysis of phenylsilane and phenylgermane, respectively. Laser-induced fluorescence (LIF) excitation and dispersed spectra of the A 1 B 1 -A 1 A 1 transition were measured for these radicals, and vibrational and rotational analyses were carried out. Heterogeneous predissociation to Si( 3 P) + H 2 is proposed from the anomalous rotational structure in the excitation spectra; the rotational lines of the p(1) subbranch ( K a = O → K a = 1) have a stronger intensity than those of the r(O) subbranch ( K a = 1 → K a = O), though the latter is expeced to be stronger due to the low temperature rotational distribution in the jet. The time-resolved excitation spectra demonstrate a shorter lifetime of K a = 1 rovibronic levels than that of K a = O levels in the A 1 B 1 state. The mechanism of the heterogeneous predissociation is discussed. The onset of the second predissociation channel yielding Si( 1 D) + H 2 is manifested at the (0,7,0) vibronic level of the A 1 B 1 state as a sharp decrease in the observed fluorescence lifetime for this level relative to that predicted for a pure radiative lifetime. The LIF spectra of the A 1 B 1 -X 1 A 1 transition of germylene were measured in the wavelength region of 514–614 nm for the first time. Vibrational analysis of the bending mode was carried out. The LIF excitation spectrum suggests the predissociation mechanism similar to that of SiH 2 is operative.