Kazuhiko Shibuya

Cryogenic neon matrix-isolation FTIR spectroscopy of evaporated ionic liquids: geometrical structure of cation-anion 1:1 pair in the gas phase.

Low-temperature infrared spectra of thermally evaporated ionic liquids, 1-ethyl- and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide and bis(trifluoromethanesulfonyl)amide have been measured in a cryogenic Ne matrix. The experimental IR spectrum of bis(trifluoromethanesulfonyl)amide can be reproduced theoretically by not B3LYP/6-31G* but MP2/6-31G* calculation, which suggests that the vibrational analysis for ionic liquids composed of bis(trifluoromethanesulfonyl)imide anion would be more successfully performed using the MP2 calculation. By comparison of the matrix-isolation spectra of the ionic liquids with the MP2 calculation, their geometrical structures in the gas phase are determined to be of C(2-position)-H(+)...N(-) interaction structure, which corresponds to the geometry of the energetically second-lowest ion-pair structure. The present study may provide a valuable clue to understand a vaporization mechanism of ionic liquid.

Infrared spectroscopy and quantum chemical calculations of OH-(H2O)n complexes.

Infrared spectra of OH-(H2O)n (n = 1, 2) isolated in solid Ne were measured by FT-IR spectroscopy. Complexes of OH-(H2O)n were prepared by vacuum ultraviolet (VUV) photolysis of water clusters, and the OH radical stretch and HOH bending vibrations of OH-H2O and OH-(H2O)2 complexes were identified with the aid of quantum chemical calculations. Observation of the recombination reaction OH-H2O + H --> (H2O)2 under dark conditions provides undisputed evidence for our spectroscopic assignment. Quantum chemical calculations predict the cyclic structure to be the most stable for OH-(H2O)2 and OH-(H2O)3. The strength of the hydrogen bond within OH-(H2O)n depends on cluster size.

Electron spin dynamics of triplet and doublet molecules in room temperature ionic liquids studied by a time-resolved EPR method

A time-resolved (TR-) EPR method was applied to measure the triplet spectra of porphyrins such as ZnTPP (TPP, tetraphenylporphyrin) and H4TPP2+ in room temperature ionic liquids (RTIL). The spectra were successfully obtained at 298 K with clear canonical peaks of the triplet sublevels. Magneto-photo selection experiments were carried out for ZnTPP in NR4BF4 (NR4: N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium) and H4TPP2+ in BmimPF6 (Bmim: 1-butyl-3-methylimidazolium). In these systems, the intensity ratio of the canonical peaks depends on the orientation between the laser polarization and the external magnetic field at the delay time on the order of submicro-seconds. This experimental finding suggests that there are very slow tumbling motions of ZnTPP and H4TPP2+ in RTILs. Electron spin polarization created in the triplet–doublet system is also successfully observed in RTILs by the TR-EPR method. Based on the analysis of the time evolution curves of both the triplet and doublet molecules, spin polarization mechanisms in the RTILs were discussed.

Jet spectroscopy of arylmethyl radicals in the visible region: assignment of low-frequency vibrational modes in diphenylmethyl and chlorodiphenylmethyl radicals

The D(1)-D(0) transitions of diphenylmethyl (DPM) and chlorodiphenylmethyl (CDPM) radicals were studied by laser induced fluorescence (LIF) spectroscopy in a supersonic jet. Laser induced fluorescence excitation and dispersed fluorescence (DF) spectra were obtained for DPM and CDPM radicals produced by ArF excimer laser (193 nm) photolyses of their chlorides. With the aid of the density functional theory (DFT) calculation, vibronic bands are assigned by comparing the observed LIF excitation spectra of the jet-cooled radicals with the single vibronic level DF spectra. Low-frequency vibrations of 55 and 53 cm(-1) in the ground and excited states, respectively, are assigned to the symmetric phenyl torsional mode of the DPM radical. The geometries of DPM in the ground and excited states are discussed with regards to observed spectra and DFT calculations. Similarly for the CDPM radical, symmetric phenyl torsional and Ph-C-Ph bending modes are assigned and the halogen-substitution effect in equilibrium geometry is discussed.