Masao Takayanagi

Conformations of nitro-substituted spiropyran and merocyanine studied by low-temperature matrix-isolation infrared spectroscopy and density-functional-theory calculation

Abstract Infrared spectrum of a spiropyran, 1 ′ ,3 ′ -dihydro-1 ′ ,3 ′ ,3 ′ -trimethyl-6-nitrospiro[2H-1-benzopyran-2,2 ′ -[2H]indole], in a low-temperature argon matrix was measured with a Fourier transformed infrared spectrophotometer. The conformation of this spiropyran was determined by comparison of the observed spectrum with a spectral pattern obtained by the density-functional-theory calculation. This conformation differs from the optimized geometry derived from an HF/6-31G* calculation. The conformations of a merocyanine produced from the spiropyran upon UV irradiation were also determined by the same method.

Photoreaction mechanisms of 2-chlorophenol and its multiple chloro-substituted derivatives studied by low-temperature matrix-isolation infrared spectroscopy and density-functional-theory calculations

Abstract Photoreaction mechanisms of 2-chlorophenol, 2,3-dichlorophenol, 2,4-dichlorophenol, 2,5-dichlorophenol, 2,6-dichlorophenol and 2,4,5-trichlorophenol in low-temperature argon matrices are investigated by Fourier transform infrared spectroscopy. The observed infrared bands of photoproducts are assigned with an aid of density-functional-theory (DFT) calculations, where the 6-31++G ∗∗ basis set is used to optimize geometrical structures. It is concluded that five-member-ring ketene, cyclopentadienylidenemethanone (CPYM), is produced through keto carbene, 2-oxocyclohexa-3,5-dienylidene, by dissociation of hydrogen chloride. The geometries of HCl–CPYM complexes in a matrix cage are derived from the vibrational shifts of the hydrogen chloride.

Isomeric structures of CH3I dimers in a supersonic jet studied by matrix-isolation infrared spectroscopy and ab initio calculation

Abstract CH 3 I in a supersonic jet was isolated in a low-temperature argon matrix. The observed infrared bands were assigned to monomer and dimers by examining dependence of the intensities on the mixing ratio with argon gas and the stagnation pressure of the supersonic jet. Ab initio calculations at the MP2 level predicted that head-to-tail (HT) and head-to-head (HH) structures of CH 3 I dimers were stable. The dimerization energy of HT obtained by a single-point-energy calculation at the MP4(SDTQ) level was 185 cm −1 larger than that of HH. A comparison of the observed and calculated wavenumbers evidences that HT and HH co-exist in the jet.

Photodissociation of acetaldehyde studied by photofragment excitation spectroscopy in a supersonic free jet

Abstract The photofragment excitation spectrum was obtained for the photochemical reaction, CH 3 CHO*→CH 3 +HCO, in a supersonic free jet, by monitoring the ∼ ← ∼ transition of the HCO radical. The collision-free measurements fix the threshold for the dissociation at 320.5 nm, corresponding to a barrier height of 51.9 kJ mol −1 on the T 1 surface of acetaldehyde. The decrease of the fluorescence quantum yield of acetaldehyde between 320.5 and 317.5 nm was found to be accompanied by an increase of the HCO yield, which was ascribed to the energy-dependent dissociation rate above the barrier.

Reaction of H2O with H produced by the 266 nm photolysis of HI

Abstract The elementary reaction, H + H2O → OH + H2, has been studied in the flowing mixture of HI and H2O irradiated at 266 nm. The nascent rotational distributions of OH are of Boltzmann-type with a remarkably non-statistical partition over the Λ-doublet sublevels, while the spin—orbit components are populated statistically. Weak dependence on the collision energy is suggested. These results are shown to be explained with a classical model based on the direct stripping mechanism with the reaction barrier at a later stage of the reaction coordinate.

Structures of CH3F CH3F and CH3F H2O complexes in a supersonic jet studied by matrix-isolation infrared spectroscopy and density-functional-theory calculation

The CH3F⋯CH3F and CH3F⋯H2O complexes produced by supersonic-jet expansion have been deposited on a cold plate using a standard matrix-isolation technique. By comparing the infrared spectra measured with an FTIR spectrophotometer with the results of DFT calculations, the structure of CH3F⋯CH3F is estimated to be anti-parallel, while that of CH3F⋯H2O has a bent C–F⋯H–O intermolecular hydrogen bonding. The difference in the structure of CH3F dimer from that of CH3I dimer is explained in terms of the dipole–dipole interaction of two methyl halide molecules and the dispersion force of halogen atoms.

N2O clusters in a supersonic jet studied by matrix-isolation infrared spectroscopy and density functional theory calculation

Abstract N2O clusters in a supersonic jet were isolated in a low-temperature argon matrix. The infrared bands of the clusters were assigned with the aid of the results of density functional theory (DFT) calculation where the 6-31+G∗ basis set is used to optimize geometrical structures. It is concluded that the N⋯O interacting antiparallel conformer is the most stable dimer. This result supports the high-resolution infrared spectroscopic study of Huang and Miller [J. Chem. Phys. 89 (1988) 5408], but disagrees with the recent matrix-isolation study of Nxumalo and Ford [J. Mol. Struct. 327 (1994) 145]. The observed dependence of cluster formation on stagnation pressure is used to examine the cooling effect on supersonic expansion.

Dual fluorescence of 4-dimethylaminopyridine and its derivatives: Effects of methyl substitution at the pyridine ring

Abstract Electronic absorption and emission spectra of 4-(dimethylamino)pyridine (DMAP), 3-methyl-4-(dimethylamino)pyridine (MDMAP), and 3,5-dimethyl-4-(dimethylamino)pyridine (TMAP=tetramethylaminopyridine) were measured in cyclohexane (nonpolar), chloroform (medium polar), and acetonitrile (highly polar) solutions. Intense charge transfer emission of DMAP was observed only in acetonitrile, while that of MDMAP and TMAP was observed in all the three solvents. Dynamics of excited electronic states of these molecules is discussed on the basis of steric hindrance between methyl groups at 3- and 5-positions of pyridine ring and dimethylamino groups.

Infrared spectra of Dewar 4-picoline in low-temperature argon matrices and vibrational analysis by DFT calculation

Abstract Dewar 4-picoline produced by UV irradiation on 4-picoline in a low-temperature argon matrix was monitored by FT-IR spectroscopy. The observed infrared bands were assigned to an isomer which has a C–C bridging bond with the aid of DFT (density functional theory) calculation, where the 6-31++G ** basis set was used to optimize the geometrical structure. No other isomer bands were observed. A systematic comparison of the scaling factors derived from the observed and calculated wavenumbers for pyridine, 2-picoline, 4-picoline and their corresponding Dewar isomers indicates a linear relationship between the scaling factors and the vibrational wavenumbers.

Infrared-induced rotational isomerization of 1,2-ethanediamine in argon matrices and conformational analysis by DFT calculation

Abstract Infrared spectra of 1,2-ethanediamine and its two deuterated species, ND2CH2CH2ND2 and NH2CD2CD2NH2, were measured by matrix-isolation FTIR spectroscopy. Isomerization around the central C–C axis from two gauche conformers to one trans conformer was found to occur upon infrared irradiation. With an aid of density functional theory, DFT, calculations, where the 6-31++G** basis set was used to optimize geometrical structures, the gauche conformers were assigned to G+G+G− and TG+G−, and the trans conformer to TTT. Wavelength dependence of the isomerization rates was examined using a tunable narrow band pass filter. It was found that relative quantum yields depend on excitation energy but not on the type of vibrational modes which absorb infrared rays.