Masaaki Fujii

OH stretching vibrations of phenol—(H2O)n (n=1–3) complexes observed by IR-UV double-resonance spectroscopy

Abstract OH stretching vibrations of jet-cooled phenol and phenol—(H 2 O) n ( n =1–3) complexes were investigated by IR—UV double-resonance spectroscopy. The stretching vibrations of the H 2 O moieties as well as that of the phenol moiety were observed for the complexes. A remarkable red-shift with increase of n was found for the phenolic OH vibration. The symmetric (ν 1 ) vibrations of the H 2 O moieties exhibit large red-shifts and splittings, while the antisymmetric (ν 3 ) vibrations show small red-shifts with small splittings. The spectral feature of the H 2 O moieties in the complexes was found to be quite similar to that of the pure (H 2 O) n . The result suggests the complexes have structures such that the hydrogen bond is formed between phenol and the (H 2 O) n clusters.

Electronic spectra of uracil in a supersonic jet

Abstract The fluorescence excitation and dispersed fluorescence spectra of uracil in a supersonic jet have been observed. The n,π∗ states of 2,4-diketo tautomer and enol-keto tautomer are found. The spectral analyses show an out-of-plane deformation of the molecules in the n,π∗ state. The coexistence of diketo and enol-keto tautomer in the vapor is discussed.

Electronic spectra of jet-cooled azulene

Abstract Fluorescence excitation spectra and dispersed fluorescence spectra of the S 2 , S 3 and S 4 S u transitions of azulene cooled in a supersonic free jet have been measured. The fluorescence excitation spectrum of the S 2 S 0 transition shows a sharp but complicated structure which can be ascribed to vibronic coupling and vibronic mixing in the S 2 state. It was found from the dispersed fluorescence spectra that above 1600 cm −1 from the S 2 origin a considerable intramolecular vibrational relaxation is occurring. The fluorescence excitation spectra for the S 3 , S 4 S 0 transitions show only broad structures and the dispersed fluorescence spectra revealed the existence of internal conversion to the S 2 state.

Predissociation of the acetylene à 1Au state and its mechanism

The fluorescence excitation spectrum, the MPI spectrum, and the absorption spectrum of acetylene were observed for the A 1Au ←X 1∑+g band system in a static gas cell and in a supersonic jet. A sudden and drastic decrease in fluorescence quantum yield, Φf , was found between the V 4 K2 (46 339 cm−1 ) and 21 V 3 K0 (46 673 cm−1 ) sublevels. The decrease in Φf is concluded to be due to the predissociation into C2 H+H. J dependence of Φf was found for the V 4 K1 vibronic sublevel, while it is absent for the level lying above V4 K1 . From the observed J dependence, the predissociation mechanism was concluded to be vibrational predissociation by tunneling through a potential barrier.

Predissociation of acetylene in à 1Au state

Abstract The fluorescence excitation spectrum, the MPI spectrum, and the absorption spectrum of acetylene due to the A 1Au←X transition were observed in a gas and in a supersonic jet. A sudden decrease in the fluorescence quantum yield Φf was found above the V4K2 (46339 cm−1) vibronic sublevel. The decrease is due to predissociation into C2H + H. A K and J dependence on Φf was also found.

Rotational energy transfer in NO (A2Σ+, v = 0 and 1) studied by two-color double-resonance spectroscopy

Abstract Collision-induced rotational relaxation in the A 2 Σ + , v = 0 and 1 states of NO has been measured by using step-wise double-resonant ionization spectroscopy. Multiple quantum rotational energy transfer is occurring to at least |Δ J | = 6 and the observed cross sections ranging from tens to hundreds of A 2 are larger than the gas-kinetic collisional cross section. The energy-transfer efficiency is slightly enhanced by the vibrational excitation. Energy-based scaling laws are successfully applied to reproduce the observed rotational distribution.

Pulsed-field-ionization spectroscopy for the study of molecular cations

Abstract It is shown that pulsed-field-ionization (PFI) spectroscopy using usual MPI apparatus without any magnetic shielding gives the spectra of molecular cations comparable to those obtained by ZEKE spectroscopy which requires a thorough magnetic shielding. The electrons detected by PFI spectroscopy were proved to come from very high Rydberg states of a neutral molecule near the convergence limit. The potential of PFI spectroscopy for the study of the vibrational structures of cations is demonstrated for the cations of DABCO, 1,2,4,5-tetrafluorobenzene and m -fluorotoluene.

Electronic spectra of o-, m- and p-tolunitrile—substituent effect on internal rotation of the methyl group

Abstract The S 1 ← S 0 fluorescence excitation spectra and the S 1 → S 0 dispersed fluorescence spectra of o -, m -and p -tolunitrile were measured in supersonic jets. Low-frequency bands due to internal rotation of the methyl group were observed in m - and p -tolunitrile. Observed band positions and relative intensities of the internal rotational bands were reproduced by a calculation using a free rotor basis set. From the analysis, the potential curve of the internal rotation was determined in both S 1 and S 0 . It was found that the barrier height increases in going from S 0 to S 1 in m -tolunitrile, while it decreases in p -tolunitrile. In contrast, no low-frequency band was found in o -tolunitrile. It is concluded that the potential curve in o -tolunitrile does not change in going from S 0 to S 1 . The change of the barrier height by electronic excitation in tolunitriles differs greatly from that observed in other toluene derivatives. It is suggested that the electronic properties of a substituent are important for the methyl rotation in the excited state.

Two-color double resonance spectroscopy via à 1Au state of acetylene : 3p Rydberg state and its Renner-Teller effect

The two‐color double resonance multiphoton ionization spectra due to the transitions from various rovibrational levels of the A 1Au state of acetylene to the 3p Rydberg state have been measured. The observed spectra showed large dependence on the quantum number K. It was concluded from the spectral analysis that the geometry of the 3p Rydberg state is linear. The spectra also showed a long progression of the trans‐bending vibration, supporting the linear structure. The trans‐bending progression belonging to the 1Δg electronic state showed the Renner–Teller splittings. The observed splittings were reproduced by the calculation using the formulas for a linear triatomic molecule in a Δ electronic state.

Direct observation of second excited 1,3 (n,π*) states of pyrazine by UV—IR double resonance dip spectroscopy

UV—IR fluorescence and phosphorescence dip spectroscopy have been applied for the observation of the second excited 1,3(n,π*) states pyrazine in the vapor. The observed state energies agree very well with those of the ab initio calculation with DZCI.