Kinichi Obi

Transient absorption, lifetime and relaxation of C60 in the triplet state

Abstract Transient absorption and time-resolved thermal lensing techniques have been used to study the photophysical behavior of C 60 in benzene solution at room temperature. After the photoexcitation with a 308 nm XeCl excimer laser, the triplet state was the only transient species detectable with the 10 ns time-resolution. The triplet—triplet absorption spectrum with apparent band peaks at 330 and 745 nm covers the whole spectral range of 290–850 nm. The triplet lifetime in air-free benzene is 49±1 μs and essentially all the photon energy absorbed is released as heat, predominantly through the triplet state.

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...

Bound–bound A 2Σ+–X 2Π transition of NO–Ar van der Waals complexes

The bound–bound excitation spectrum of the NO–Ar van der Waals complex associated with the NO A 2Σ+–X 2Π transition has been measured by the resonance enhanced two‐photon ionization (RE2PI) method using a time‐of‐flight (TOF) mass spectrometer. The van der Waals bands characterized by red‐shaded rotational contours present no regularity in the progression. The photodissociation action spectra obtained by probing the NO A 2Σ+(v’=0, N’=1–8) products have also been measured, and the binding energies (D0) of the complex in the A 2Σ+ and X 2Π states are determined as 44 and 88 cm−1, respectively. The action spectrum corresponding to the NO A 2Σ+(v’=0, N’=1 and 2) product shows several shape resonance peaks, which implies that the intermolecular potential between NO A 2Σ+ and Ar has a potential barrier of about 24 cm−1.

Dynamics of the reactions of O(1D) with HCl, DCl, and Cl2

The reactions O(1D)+HCl→OH+Cl (1a) and OCl+H (1b), O(1D)+DCl→OD+Cl (2a) and OCl+D (2b), and O(1D)+Cl2→OCl+Cl (3) are studied at an average collision energy of 7.6, 7.7, and 8.8 kcal/mol for (1), (2), and (3), respectively. H, D, and Cl atoms are detected by the resonance‐enhanced multiphoton ionization technique. The average kinetic energies released to the products are estimated from Doppler profile measurements of the product atoms. The relative yields [OCl+H]/[OH+Cl] and [OCl+D]/[OD+Cl] are directly measured, and a strong isotope effect (H/D) on the relative yields is found. The fine‐structure branding ratios [Cl(2P1/2]/[Cl(2P3/2)] of the reaction products are also measured. The results suggest that nonadiabatic couplings take place at the exit channels of the reactions (1a) and (2a), while the reaction (3) is totally adiabatic.

Ã→X̃ fluorescence spectra of CH3O and C2H5O generated by the Arf laser photolysis of alkyl nitrites

Abstract The A → X system fluorescence spectra of CH3O and C2H5O have been obtained following the 193 nm photolysis of methyl and ethyl nitrites. These species are produced in highly rotationally and vibrationally excited states. The OO band is at 31530 cm−1 for CH3O and at 29200 cm−1 for C2H5O. The collision-free fluorescence lifetimes of the A state are independent of the levels of the CO stretching vibrational mode and are measured to be 2.2 μs for CH3O and 1.8 μs for C2H5O. The quenching rate constants by the parent molecules show a little increase with the levels of the CO stretching vibrational mode. The vibrational distribution in the photofragments is discussed using statistical models.

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 A 1B1−X 1A1 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 A 1B1 state.The heterogeneous predissociation is interpreted with the second order perturbation: A 1B1 –(a‐type Coriolis)→X 1A1 ‐(spin–orbit)→a 3B1→Si(3P)+H2. It is demonstrated experimentally that there is a potential barrier associated with the dissociation path of a 3...

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.

Laser induced fluorescence of NH2(Ã 2A1) in the supersonic free jet

The fluorescence excitation spectra of the NH2 A 2A1←X 2B1 transition have been measured in the supersonic free jet. The rotational cooling of the ground state NH2 radical results in the observation of only the Π vibronic subbands in the excitation spectra. The fluorescence lifetimes are obtained for single rovibronic levels of the A 2A1 state in the jet. The radiative lifetime is shortened from 10.3 μs for Π(0,8,0) 11,0 to 4.4 μs for Π(0, 14, 0) 11,0 with decreasing the excitation wavelength, which is explained by the cubic transition energy dependence of the Einstein A coefficient. Little difference is observed between the lifetimes of the spin components belonging to the same rotational level and between those of the Fermi resonance pairs. The transition moment of the A 2A1–X 2B1 transition is experimentally determined to be 0.037±0.004e2α20.

Ion desorption from H2O chemisorbed on Si(100) by O 1s electron excitation at room temperature

The photon stimulated ion desorption (PSID) of H+ and O+ from monolayer H2O adsorbed on the Si(100) has been studied using pulsed synchrotron radiation in the 510–620 eV range. Ions were detected and mass analyzed by means of time‐of‐flight spectroscopy. Relative yield spectra of these ions indicated characteristic behavior near the O K edge. The predominant H+ fragment ion shows a sharp rise at about 530 eV and two broad peaks (535 eV, 558 eV), while O+ shows a delayed threshold at about 570 eV and gradual increase up to 700 eV. Above the O K edge, these ion yields were found to deviate significantly from the O(KVV) Auger electron yield. This was interpreted by the fact that ion desorption was enhanced by multiple ionization and is strongly affected by the decay process with the surface. In order to elucidate the mechanism of the PSID, the technique of photoion–photoion coincidence between H+ and O+ ions was also applied. The results suggested the formation of multiply charged intermediates, i.e., OH4+ i...

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 1 2A2–D0 1 2B1 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.