Ichiro Hanazaki

The S1(n, π*) states of acetaldehyde and acetone in supersonic nozzle beam: Methyl internal rotation and C=O out‐of‐plane wagging

Fluorescence excitation spectra of CH3CHO, CH3CDO, (CH3)2CO, and (CD3)2CO have been observed in an Ar supersonic nozzle beam. Vibrational analyses have been performed for vibronic bands in the region at wavelengths longer than 313 nm. The 0–0 bands of the S1(n, π*) states were located at 29 771, 29 813, 30 435, and 30 431 cm−1, respectively. The spectra could be analyzed taking the C=O out‐of‐plane wagging and the CH3 internal rotation as active modes. By fitting a double minimum potential function to the observed vibrational levels, it has been shown that these molecules are pyramidally distorted in the S1(n, π*) state with barrier heights to inversion of 541, 578, 468, and 480 cm−1, respectively. Similar analyses using the Mathieu function gave threefold potential functions for the methyl internal rotation with barrier heights to rotation of 691, 645, 740, and 720 cm−1 for CH3CHO, CH3CDO, (CH3)2CO, and (CD3)2CO, respectively. High resolution measurements of rotational envelopes have shown that the out‐o...

The S1, 1A2(n,π*) state of acetone in a supersonic nozzle beam. Methyl internal rotation

Abstract Fluorescence excitation spectra of the S 1 , 1 A 2 (n, π*) state of acetone and acetone- d 6 have been measured. Active vibrational modes are the CH 3 torsion and the CO out-of-plane wagging. The barriers to internal rotation, V 3 , for acetone and acetone- d 6 in the S 1 state have been estimated to be 740 ± 90 and 720 ± 60 cm −1 , respectively.

Photo-inhibition of chemical oscillation in the Ru (bpy)2+3-catalyzed Belousov-Zhabotinskii reaction

Abstract The wavelength dependence of photo-inhibition is reported for the Ru(bpy) 2+ 3 -catalyzed Belousov—Zhabotinskii (BZ) reaction. Use of the critical light power, P c 0 , and the relative cross section, σ R , makes it possible to discuss the inhibition mechanism quantitatively. On the basis of the observed dependences of σ R and P c 0 on wavelength and on the concentration of Ru(bpy) 2+ 3 , together with related observations of the effects of irradiation on the Br − concentration and on the BZ system without substrate, the primary step and the following processes in the inhibition phenomenon are discussed, with some newly proposed reaction schemes.

The S1(n,π*) states of cyclopentanone and cyclobutanone in a supersonic nozzle beam

Fluorescence excitation spectra of cyclopentanone and cyclobutanone have been observed for their (n,π*) transition in a pulsed supersonic nozzle beam using a high power tunable laser. A drastic reduction of hot bands has been attained, making it possible to discuss the vibronic assignments in more detail than the previous works. The C=O out‐of‐plane wagging mode was found to be active for both molecules. The ring twisting and flapping in cyclopentanone and the ring puckering in cyclobutanone were also active. The molecules are pyramidally distorted in the excited states with double minimum potentials in the out‐of‐plane displacement coordinates. The barrier to inversion (V) and the C=O out‐of‐plane angle at the potential minimum (θm) have been determined for the S1(n,π*) state; V=680±17 cm−1 and θm=34° for cyclopentanone, and V=1850±50 cm−1 and θm=42° for cyclobutanone. The puckering mode (ν20′) of cyclobutanone was also found to have a double minimum potential with V=16.9 cm−1. The rotational envelope of...

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.

Abinitio study of the methyl internal rotation of acetaldehyde in the S1 (n ,π*) state

Ab initio SCF calculations have been performed on the methyl internal rotation of acetaldehyde in the S1 (n, π*) state as well as in the ground state. The calculated barrier heights to methyl rotation (481 and 732 cm−1 for the ground and S1 states, respectively) are in good agreement with experimental values. The Mulliken population analysis has revealed that the ‘‘group’’ overlap population between the methyl and formyl groups correlates very well with the potential curve for methyl rotation, suggesting that the intergroup bonding governs the potential curve. It is also shown that the intergroup π bonding (hyperconjugation) is important in determining the barrier. The change of the stable conformation from the H eclipsing O type in the ground state to the ‘‘H antieclipsing O’’ conformation in the S1 state is shown to be due to the presence of an antibonding π electron in the latter.

Intermolecular dynamics and exciplex formation of the 1‐cyanonaphthalene/triethylamine van der Waals complex

The exciplex formation dynamics of the 1‐cyanonaphthalene/triethylamine van der Waals complex upon excitation has been examined under collision free conditions. Mode‐specificity has been found in the excitation of a combination band between intra‐ and intermolecular vibrational modes in the S1 state of the vdW complex to promote the exciplex formation reaction. The specificity is lost at higher excess energies since randomization of energy among intermolecular modes is more extensive than the reaction rate. The fluorescence decays of the S1 and exciplex states have been measured as a function of excess vibrational energy above the S1 origin. The lifetime of the S1 state at the excess energy where the mode‐specific reaction is observed is different from that of the exciplex fluorescence. As the excess energy increases, the decay rate of the S1 state shows a sharp increase due to the exciplex formation while the exciplex fluorescence rate remains constant. The observed decay rate constants have been discuss...

Fluorescence-dip and stimulated-emission-pumping laser-induced-fluorescence spectra of van der Waals molecules containing benzonitrile

Fluorescence-dip spectra of benzonitrile and some van der Waals complexes containing benzonitrile (benzonitrile dimers, benzonitrile–Ar, and benzonitrile–H2O) were measured. The vibrational bandwidths in the fluorescence-dip spectra were found to be determined by the rotational structure and not by the rate of vibrational dissociation of the complex or by the rate of vibrational relaxation into the intermolecular modes. Stimulated-emission-pumping (SEP) laser-induced-fluorescence (LIF) spectra were also measured to permit the study of the dynamical behavior of the complexes. The relaxation of the vibrational states (ν10, ν12, and ν10 + ν12 of benzonitrile) prepared by SEP was probed directly by varying the delay between the SEP and LIF laser pulses. The monomer showed slow decay, which could be due to the escape of the vibrationally excited species out of the probe region. On the other hand, the dimer showed no detectable LIF signal, indicating fast relaxation of the prepared vibrationally excited state. Finite decay rates were obtained for benzonitrile–Ar and benzonitrile–H2O, which were not sensitive to the vibrational energy. Some advantages of using the fluorescence-dip and SEP-LIF techniques in the study of vibrational spectroscopy and the dynamics of van der Waals complexes are pointed out and discussed.

Asymmetric coupling stabilizes the out-of-phase mode : experimental evidence in the Belousov-Zhabotinsky reaction

Abstract The Belousov—Zhabotinsky reaction was studied for the system with two continuous-flow stirred tank reactors coupled to each other through mass transfer. The coupling strength was quantitatively controlled by changing the flow rate between the reactors with a peristaltic pump. It became clear that when the coupling between the reactors was symmetric, synchronization or entrainment with the in-phase mode was quite stable. On the other hand, the parameter space, or the basin, of the out-of-phase mode became greater with “asymmetric” coupling. Such an experimental trend is discussed in relation to the results of numerical simulations on coupled nonlinear differential equations.

Photoinduction and photoinhibition of chemical oscillations in the tris(2,2′-bipyridine) ruthenium (II)-catalyzed minimal bromate oscillator

Abstract The tris (2,2′-bipyridine) ruthenium (II)-catalyzed minimal bromate oscillator is shown to exhibit the chemical oscillation similarly to the system with other catalysts. The photoresponse of the minimal oscillator has been investigated for the first time to show both induction and inhibition of sustained oscillations. It has been found that [Br−] tends to decrease not only in the photoinduction but also in the photoinhibition of chemical oscillation, in contrast to the previous view for the photoinduced pattern formation in the full Belousov-Zhabotinsky system. This result may require more detailed investigation for the latter system.