Mitsuo Tasumi

Asynchronous Time-Resolved Fourier Transform Infrared Spectroscopy

A novel asynchronous time-resolved FT-IR spectrophotometer based on a conventional continuous-scan interferometer has been developed. In contrast to the existing methods, this method does not require the synchronization between the signal for time resolving and that for the sampling of the A/D converter. The signal-processing assembly for time-resolved measurements consists of a pulse generator, a pulse delay circuit, a gate circuit, and a low-pass filter. This assembly can be attached to any conventional FT-IR spectrophotometer. By this method, time-resolved spectra without any spectral distortion or artifacts can be obtained for repetitive fast phenomena. As an application of this method, time-resolved FT-IR measurements have been carried out for the reorientation process in a ferroelectric liquid crystal induced by the reversal of external electric field, and a time resolution of 0.5 μs or less has been achieved. The present system is best suited for observing repetitive transient phenomena with lifetimes in the range from approximately 1 μs to 1 ms.

Fermi resonance in CO2: A combined electronic coupled-cluster and vibrational configuration-interaction prediction

The authors present a first-principles prediction of the energies of the eight lowest-lying anharmonic vibrational states of CO(2), including the fundamental symmetric stretching mode and the first overtone of the fundamental bending mode, which undergo a strong coupling known as Fermi resonance. They employ coupled-cluster singles, doubles, and (perturbative) triples [CCSD(T) and CCSDT] in conjunction with a range of Gaussian basis sets (up to cc-pV5Z, aug-cc-pVQZ, and aug-cc-pCVTZ) to calculate the potential energy surfaces (PESs) of the molecule, with the errors arising from the finite basis-set sizes eliminated by extrapolation. The resulting vibrational many-body problem is solved by the vibrational self-consistent-field and vibrational configuration-interaction (VCI) methods with the PESs represented by a fourth-order Taylor expansion or by numerical values on a Gauss-Hermite quadrature grid. With the VCI, the best theoretical estimates of the anharmonic energy levels agree excellently with experimental values within 3.5 cm(-1) (the mean absolute deviation). The theoretical (experimental) anharmonic frequencies of the Fermi doublet are 1288.9 (1285.4) and 1389.3 (1388.2) cm(-1).

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.

Analysis of the absorption spectrum (1 1Bu←1 1Ag) and resonance Raman excitation profiles of trans‐1,3,5‐hexatriene based on ab initio molecular orbital calculations

The electronic absorption spectrum, the relative Raman intensities upon 0‐0 excitation, and the resonance Raman excitation profiles of trans‐1,3,5‐hexatriene in the region of the 1 1Bu←1 1Ag transition are analyzed on the basis of the structures and vibrational force fields obtained from ab initio molecular orbital (MO) calculations. The second‐order Mo/ller–Plesset perturbation (MP2) and the configuration interaction singles (CIS) methods are employed to describe the 1 1Ag and 1 1Bu states, respectively. The vibrational force fields obtained from ab initio MO calculations are scaled in order to fit the calculated frequencies to the observed. The Duschinsky rotation among all the modes of ag symmetry is fully taken into account. Both the calculated absorption spectrum and resonance Raman intensities are in agreement with the observed. This shows the usefulness of the CIS method for estimating the structure and vibrational force field in the 1 1Bu state of trans‐1,3,5‐hexatriene. On this basis, some refine...

Excitation energy transfer from symmetric cyanine dyes to unsymmetric merocyanine aggregated in functionalized Langmuir–Blodgett films by time-resolved fluorescence spectroscopy

Abstract The fluorescence decays and ultrafast time-resolved spectra in mono- and multilayered Langmuir–Blodgett (LB) films were measured to explore the dynamics of excitation energy transfer between the monomer and aggregates of symmetric and unsymmetric cyanine dyes. J- and H-aggregate formation of a long-chain merocyanine dye depends upon the constituent of the molecular matrix. Steady-state and time-resolved spectroscopic studies of these dyes embedded in suitably designed monolayer assemblies revealed that a monomeric cyanine fluorescence is quenched by the aggregates of the merocyanine in the fatty acid–octadecane ternary system, indicating efficient energy transfer mechanism from the monomeric cyanine to the J-aggregates of merocyanine via the H-aggregates.

Correlation between redshifts and widths of the 0–0 band in the absorption spectra (1 1Bu←1 1Ag) of all‐trans‐β‐carotene in solution

The wave numbers and widths of the 0–0 band in the electronic absorption spectra (1 1Bu←1 1Ag) of all‐trans‐β‐carotene in various solvents at room temperature are analyzed. These quantities are obtained with sufficient precision from the broad absorption spectra by performing simulations with the parameters obtained in our previous work. The excess redshifts for various solvents (deviations from the linear relationship between the 0–0 wave number and the Bayliss parameter obtained for alkane solvents) are found to be correlated with the 0–0 band widths. To explain this correlation quantitatively, a theoretical model is developed by introducing a low‐frequency collective solvent mode, which changes significantly the microscopic polarizability of solvent. This model is consistent with the experimental result that excess redshifts can be observed in nonpolar as well as polar solvents. It is pointed out that the small Stokes shifts observed for β‐carotene in nonpolar solvents can also be explained by this model.

The 1320-nm Excited FT-Raman Spectra of Lightly Iodine-Doped trans-Polyacetylene

The FT-Raman spectra oftrans-polyacetylene films doped lightly with iodine were obtained with the 1320-nm laser line. The observed Raman bands are attributed to positively charged domains created by acceptor doping. The observed Raman wavenumbers of the ν2 (CC stretch), ν3 and ν4 bands (mixed of CC stretch and CH in-plan bending)|of iodine-doped form are slightly higher than those of the corresponding bands of pristinetrans-polyacetylene, whereas the contrary is the case for ν1 band (C=C stretch)|of iodine-doped form. In particular, these upshifts of the ν2 and ν3 bands are distinguished from the downshifts of these bands in donor doping. The origin of doping induced Raman bands is discussed in terms of solitons and polarons.

Transient vibrational temperatures estimated from anti-Stokes and Stokes Raman intensities and vibrational cooling of electronically excited trans-stilbene in solution

To examine vibrational cooling of trans-stilbene in the S1 state, transient temperatures of a few vibrational modes were estimated by analyzing transient anti-Stokes and Stokes Raman intensities. Vibrational temperatures obtained for the olefinic C = C and C–Ph stretches are 900 and 680 K, respectively, at 0 ps after photoexcitation (temporal resolution ca 5 ps). These values are higher than the equilibrium temperature (ca 550 K) calculated for a statistical distribution of excess vibrational energy. Ultrafast intermolecular energy flow (vibrational cooling) is discussed based on a model analysis. Copyright

Observation of Picosecond Transient Raman Spectra by Asynchronous Fourier Transform Raman Spectroscopy

Asynchronous Fourier transform (FT) Raman spectroscopy with 100 picosecond time resolution has been developed. A signal-processing assembly required for time-resolved and transient Raman measurements consists of a picosecond Nd:YLF laser system, a gate circuit, and a low-pass filter, and it can be attached to any conventional continuous-scan FT-Raman spectrophotometer. The principle of signal processing employed in this method is almost the same as that of asynchronous pulsed-laser-excited FT-Raman spectroscopy. This method does not require synchronization between Raman excitation by probe laser pulses and sampling by the analog-to-digital converter. Transient Raman spectra have been obtained from the first excited singlet state of three anthracene derivatives in cyclohexane solutions and photoexcited poly(p-phenylenevinylene) [(C6H4CH=CH) n ] by using 351 nm light (pulse width ã 70 ps) for photoexcitation and 1053 nm light (pulse width ã 100 ps) for Raman excitation.

Infrared Qualitative Analysis Automated by Use of an Electronic Computer and a Spectral Data File with Band Intensity Information

An infrared date file with intensity information has been prepared, based on the first 5000 spectra of the data cards of the Infrared Data Committee of Japan (IRDC). A computer program has been developed for the qualitative analysis of binary mixtures using this data file. The program has been applied to 11 binary mixtures; for ten of them it has provided correct answers among the first three compounds outputted by the computer. The computer time necessary for the analysis of a sample mixture was approximately 1 min in TSS mode, excluding the time for the input and output of data. The one unsuccessful case has been proved to be due to the unusual character of the infrared spectrum of one of the components (C2Cl6). Hence this failure does not indicate any serious defect in the program; the developed program has proved to be of practical use.