Search

Multicolor multistep photoisomerization process of azobenzene derivative in photostationary state was observed by newly developed Fourier transform two-dimensional (2D) spectroscopic technique. The photostationary state was generated by excitation using white light covering the entire visible region, and the photoreaction was monitored by measuring photoinduced bleaching and absorption signals detected by white light probe. The wavelength participating in excitation process for the observed signal was clarified by modulation frequency marked by passing the pump white light through a scanning tandem Fabry-Perot interferometer, and the 2D amplitude and phase spectra were obtained by Fourier transform of the obtained 2D interferogram. By using the system, we succeeded in observing the multicolor multistep process in photoisomerization of Sudan red 7B [1-(4-[Phenylazo]phenylazo)-2-ethylaminonaphthalene, SR7B] that has two azo groups and shows several configurations. It was concluded from the analysis of obtained 2D amplitude and phase spectra that at least two reaction pathways of sequential photoisomerization reactions exist in the photostationary state of SR7B under the white light irradiation. The interpretation is supported by the results of quantum chemical calculations using density functional theory.

The reaction pathways for photo- and thermal isomerization in the photostationary state of Sudan red 7B (SR7B), which has two azo groups in its molecule, were examined by a laboratory-designed two-dimensional millisecond time-resolved transient absorption spectrometer that utilizes two-color cw lasers (532 nm and 650 nm) as pump and a white light as probe. The temporal population behavior of four isomeric forms after the two-color pump lasers were simultaneously switched off was monitored in terms of transient absorption change with the time resolution of 50 ms. It was found that, in the photostationary state generated by the two-color pump scheme, the two-color two-step photoisomerization process and the multistep thermal isomerization processes occurred. The reaction rates of the thermal isomerization processes were also determined. Based on the results, we constructed a framework for the reaction pathway network in the photostationary state of SR7B under two-color cw excitation.

To understand the elementary steps of chemical reactions, unimolecular reactions are important and considered to be model reactions. We carried out pump–probe and two-pulse correlation (2PC) measurements of the multiphoton-induced reaction of DTTCI (3,3′-diethyl-2,2′-thiatricarbocyanine iodide), a kind of cyanine dyes, under the red-tail excitation condition and found that both photoisomerization and photodegradation were caused by a two-photon process and the reaction time for photoisomerization was approximately 0.5 ns. Excitation dynamics was examined by 2PC measurements and the temporal character of the intermediate state was analyzed.

We propose a new modulation technique for phase-sensitive detection to extract a cross-term signal appearing in multi-pulse experiments and demonstrate the selective detection of cross-term signal on two-pulse correlation measurements. This modulation technique can be widely applied to the selective detection in multi-beam laser experiments such as two-pulse correlation, auto-correlation, and double-resonance experiments, because the selectivity can be realized by using a conventional single-frequency mechanical chopper and 2f phase-sensitive detection. The effectiveness of the proposed technique was confirmed by two-pulse correlation measurements of two-photon-excited fluorescence from rhodamine 6G. In addition to the selective observation of a correlation peak, the technique succeeded in observing a weak correlation background. By combining asymmetric, two-pulse correlation measurements with the proposed technique, it was clarified that the background was produced by a three-photon process and assigned to fluorescence depletion caused by an up-conversion process. The results indicate that the cross-term selective, two-pulse correlation method that is based on the phase-shifted parallel modulation technique is powerful tool to find and analyze a high-order optical event buried in a low-order optical event.

In cyanine dye, photoisomerization paths involving multiphoton processes were found by two-color two-pulse correlation of ultrafast transient absorption spectroscopy. The reaction efficiency depended on the interval between two pump pulses, UV and NIR pulses, as well as the fluence of the NIR pulse, but was little dependent on that of the UV pulse. These results indicate that the new photoisomerization paths involve the NIR multiphoton process and/or the UV one-photon process. The difference in two-pulse correlation between positive and negative time regions revealed a new reaction path that had the highest branching ratio of cis isomer to other leuco forms.

In cyanine dye, a photo-isomerization path involving a multiphoton process was found in addition to a conventional reaction path with a one-photon process by two-pulse correlation of transient absorption and bleaching. That photo-isomerization was completed within 3 ns and its efficiency was dependent on the interval time between two pump pulses indicate that the new path involves a multiphoton process: S 0 → S n → S m , where S n is ∼3.1 eV and S m is ∼4.7 eV higher than S 0 and the lifetime of intermediate state in S n is approximately 0.2 ps. Changing the pump power controlled the branching ratio between the two paths.

Persistent organic pollutants (POPs) are toxic chemicals that adversely affect human health and the environment around the world. The detection and evaluation of small amounts of POPs require methods with both high precision and high chemical selectivity. Conventional methods involve a number of preparatory steps and time-consuming analysis and are not suitable for the abovementioned purposes. Hence, new automated analysis methods are required for on-line detection and rapid analysis of POPs. In this paper, mass spectrometry with resonance-enhanced multi-photon ionization (REMPI) is performed to obtain information about the automated analysis of POPs in the gas-phase with on-line detection. Dynamic trapping time-of-flight mass spectrometry (TOFMS) was performed with sufficient selectivity and sensitivity for rapid analysis of polychlorinated biphenyls (PCBs) in the gas phase. Compared to normal trapping, the use of dynamic trapping enabled ion signal intensity to be increased by a factor of greater than 10. The detection limit at 1 min was

This study demonstrates the applicability of laser mass spectrometry for safety management of the processed gas and the work environment in a polychlorinated biphenyl (PCB) disposal plant. By utilization of laser ionization/ion trapping storage/time-of-flight mass spectrometry (LI-IT-TOFMS), we analyzed gaseous PCBs from scrap capacitors with on-line detection. It was confirmed that few contaminants were detected in the spectrum. By the effect of laser-induced selective ionization, it was considered that there was little interference with the mass range of PCBs. The accuracy of LI-IT-TOFMS when analyzing environmental gas was almost the same as that for the PCB standard gas. It was possible to perform on-line analysis of the work environment for over 2000 h (120 000 data points). LI-IT-TOFMS was thus shown to be a very useful method for ensuring the safety of the work environment in disposal plants for PCBs.

The photochemical properties of pincer platinum complexes bearing secondary thioamide groups have been examined. The presence of the coordinated secondary thioamide linkage in the pincer ligand was found to work as a reactive site upon addition of bases and anions and to result in modulating absorption and emission properties of the complexes.

The catalytic behavior of ultrathin titanium oxide films deposited on platinum (111) surfaces is investigated through sum frequency generation (SFG) spectroscopy of the adsorption and decomposition of formate. TiOx films of 7 A or less in thickness are prepared on Pt(111) substrates by evaporation of titanium under oxygen, and samples are examined as-prepared or after annealing at 873 or 973 K. Formate is adsorbed to the samples by exposure to 1000 langmuir of formic acid at 250 K. The frequency of the stretching vibration (ν(C−D)) of the deuterated formate C−D bond is found to be sensitive to the interaction between the adsorption sites and formate. SFG observations under different polarization combinations reveal that most formate is adsorbed to the surface with a bridge configuration, and that only a small amount of monodentate formate is present on the surface of TiOx/Pt(111) annealed at 973 K. Investigation of the effect of annealing temperature, time, and atmosphere on formate ν(C−D) frequency and i...

Utilization of the picosecond (100 ps) laser ionization was successful in measuring the mass spectra attributed to di-, tri-, tetra-, penta-, and hexa-chlorinated biphenyls. It was confirmed that the quantitative limit of this method in real-time (1 min) was 10 μg/m3N (equivalent to 1/10 of the value established as the statutory limit for PCBs in the ambient air of the workplace environment). Further evaluations of measurement accuracy based on comparisons with the results of the conventional method (gas sampling and GC-MS) demonstrated a coefficient of variation within 30%. We undertook the measurement of the exhaust gas and the work environment atmosphere in PCBs treatment plants using the LI-IT-TOFMS method, confirming that the monitoring system could be operated appropriately by the introduction of an internal standard gas (2,4-dichlorinated toluene), and that it was possible to make continuous long-term measurements for over 500 h (total measurement time, >6000 h).

Effective prevention from the leakage of Polychlorinated Biphenyls (PCBs) requires the rapid analysis with on-line detection, but conventional methods require extensive analytical time (several days per sample) and are thus unsuitable. The objective of the research reported here was to develop the Laser Ionization / Ion Trap Storage / Time of Flight Mass Spectrometry (LI-IT-TOFMS) capable of monitoring PCBs within 1 min/sample, as applied to exhaust gas and the atmosphere of the disposal work environment. The achievable PCBs sensitivity for on-line measurement was found to be in the pptV range (< 0.01 mg/m3N) by means of comparison with conventional gas sampling and gas chromatograph - mass spectrometry (GC-MS). A satisfactory proportional relationship was confirmed between laser-based and conventional results for PCBs. We measured the exhaust gas in a PCBs treatment plant (hydrothermal decomposition and container treatment processes) by using the PCBs monitoring system, confirming that PCBs monitoring is possible without interference from either the main gas composition or minor coexisting substances. Accordingly, the LI-IT-TOFMS method is a useful method for the trace analysis of PCBs in exhaust gas.

A Fourier transform two-dimensional fluorescence excitation spectrometer (FT-2DFES) was developed based on the multiplex technique using a tandem Fabry-Perot interferometer (tandem FPI). In addition to the advantage of the multiplex technique, the main advantage of the tandem FPI is applicable to the modulation of transition with a large absorption bandwidth (larger than 100 nm) and is thus applicable to the modulation of the excitation of molecules in the condensed phase. As a demonstration of the effectiveness of FT-2DFES, we succeeded in separately observing the fluorescence excitation peaks from a mixed methanol solution of laser dyes (coumarin 480, rhodamine 6G, DCM (4-dicyanomethylene-2-methyl-6-(p-(dimethylamino)styryl)-4H-pyran), and LDS750). Furthermore, the energy transfer from rhodamine 6G to LDS750 was observed.

Starting from 5-methyl-1,3-bis(anilinothiocarbonyl)benzene (1), two types of luminescent pincer platinum complexes with κ3S,C,S and κ3N,C,N coordination modes were obtained. Reaction of 1 with K2PtCl4 afforded a pincer Pt(II) complex (3) with the κ3S,C,S coordination mode, whereas oxidative cyclization of 1 yielded 5-methyl-1,3-bis(benzothiazol-2-yl)benzene (2), which provided a pincer Pt(II) complex (4) with the κ3N,C,N coordination mode. Molecular structures and photochemical properties of the complexes have been examined. The decay lifetimes of the emission from the complexes were in the range 10-5−10-6 s, which were indicative of phosphorescent emission.

Two novel salts of lacunary tungstosilicates with guanidinium and alkali metal cations, (CH6N3)7Na[SiW11O39].(CH3)2CO.8H2O (1) and (CH6N3)K6Na[SiW11O39].11.5H2O (2), have been synthesized and their crystal structures have been determined by synchrotron X-ray diffraction. In both crystals, the Na+ cations link the lacunary Keggin-type tungstosilicate anions into linear structures. The neighboring [SiW11O39]8- anions are related by two-fold screw and translational operations in compounds 1 and 2, respectively. Second harmonic generation was observed for compound 1.

LI-IT-TOFMS (laser ionization/ion-trap storage/time-of-flight mass spectrometry) is expected to be a powerful tool for environmental monitoring. In the research reported here, real-time LI-IT-TOFMS measurements were carried out on gaseous 2-4 chlorinated PCBs in order to evaluate the applicability of an environmental monitoring method. With respect to ion-trap storage for PCBs, we found that the effect was due to the driving RF voltage on the ring electrode in the ion trap. For PCBs ions produced by laser irradiation, we observed that it was more efficient to reach the center of the ion trap by using a gated RF voltage rather than by using a continuous RF voltage. The ion trajectories in the ion trap were simulated by SIMION 7.0. We found that the voltage of the exit end cap electrode affected both the number of ions trapped and the orbit of ions inside the trap cell. Optimization of this parameter was performed using both simulated and experimental results. The achievable PCBs sensitivity for real-time (1 min) measurement using the LI-IT-TOFMS method was found to be in the pptV range (

The reaction dynamics of trans-2-butene adsorbed to acidic hydroxyl groups on the surface of ferrierite zeolite is examined by time-resolved spectroscopy using a tunable infrared picosecond pulse laser system. The transient absorption spectra measured by a two-color pump−probe technique at 188−243 K reveal bleaching and hot bands of the OD stretching mode 2 ps after excitation. This vibrationally excited state relaxes within 20 ps at 188 K, while the bleaching band includes a long-lifetime component that lasts for more than 100 ps at 243 K. Thus, the OD (isotope-exchanged hydroxy groups) stretching band does not entirely recover in this period and is mirrored by an analogous weakening of the CH bending band of the adsorbed trans-2-butene. Simultaneously, three new bands in CH stretching region were observed at 3045, 3095, and 3130 cm-1. This result suggests the presence of a short-lived intermediate formed by reaction between the acidic hydroxyl groups and adsorbed trans-2-butene.

Two types of energy transfer in pi-conjugated polymers have been investigated using time-resolved photoluminescence (PL) techniques: type i, perpendicular-type energy transfer from the 2,3-di(p-tolyl)quinoxaline unit to the pi-conjugated main chain of poly[2,3-di(p-tolyl)quinoxaline-5,8-diyl], and type ii, parallel-type energy transfer from the oligo(pyridine-2,5-diyl) (O-Py) unit to the oligo(selenophene-2,5-diyl) (O-Se) unit in a block-type copolymer of O-Py and O-Se. Both types of energy transfer were very fast with a time constant shorter than approximately 0.1 ns; in particular, the type ii energy transfer took place with a time constant of approximately 5 ps. Both pi-conjugated polymers were considered to contain segments with various effective pi-conjugation lengths, and the energy transfer to the segment with a larger effective pi-conjugation length and a smaller pi-pi* transition energy required a longer transition time. A polarizing film was obtained by utilizing the perpendicular-type energy transfer.

We have investigated olefins adsorbed on Bronsted acidic hydroxyl groups (OD) of DM20 zeolite by transient infrared absorption spectra after excitation of the OD stretching mode using picosecond infrared lasers. The olefins studied were ethylene, deuterated ethylene, propylene, and isobutene, and only isobutene was adsorbed on OD at its methyl group while the other olefins were adsorbed at their double bonds. For all the olefins except isobutene, simple vibrational relaxation of the v = 1 state was observed and the lifetimes were 2−4 ps. These lifetimes are an order faster than that of isolated OD. For isobutene, a long lifetime component lasting more than 500 ps was observed in addition to vibrational relaxation of 2 ps. The transient absorption spectra for isobutene-adsorbed zeolite at various time delays and frequencies indicated the existence of a short-lived species and a slow desorption process compared with vibrational relaxation.

The c(4×2)-CO/Ni(111) surface under pulsed near-infrared irradiation is examined by time-resolved sum-frequency generation (SFG) spectroscopy. At a surface coverage of 0.5, the surface is confirmed to consist almost exclusively of hollow CO molecules, as evidenced by a sole SFG peak at 1904 cm-1. Under pulsed irradiation, this peak weakened, followed by the emergence of a new peak attributable to atop CO. This represents a direct observation of site-hopping of adsorbed CO. The hopping phenomenon was found to be entirely transient, with the surface returning to the pre-excited state within a few hundred picoseconds without desorption. The dynamics of the process are also discussed.

Optical control of excited states of α-perylene crystal was realized by a femtosecond optimized pulse shaping method using Genetic Algorithm (GA). We succeeded in controlling the emission spectral feature of an α-perylene crystal; the intensity of E-emission was increased by a factor of 1.4 without the change of Y-emission intensity. Furthermore, we found a near-infrared pulse shape whose multi-photon excitation efficiency is larger than that of a single femtosecond pulse by a factor of two. On the auto-correlation traces of these shaped pulses, the several satellite peaks appeared beside the main peak. The origin and mechanism of the attained change were discussed.

The transient response of 10 molecular layers of D 2 O ice on CO/Pt(1 1 1) at 130 K was investigated under ultra-high vacuum following a near-infrared pump pulse of 35 ps by sum frequency generation (SFG) spectroscopy. The D 2 O molecules in the ice crystalline layer formed an amorphous or liquid-like structure in response to the pumping without desorption of D 2 O to the gas phase, and the crystals returned to the crystal structure on a sub-nanosecond time scale.

The IR–visible sum-frequency generation (IVSFG) method was used to perform time-resolved vibrational measurements of CO/Pt(1 1 1). Irradiation of intense picosecond laser pulses (35 ps, 1064 nm) resulted in a drop in intensity, redshift, and broadening of the on-top CO stretching peak, followed by recovery to the original peak shape on the order of hundreds of picoseconds. The transient behavior of the CO stretching signal was found to depend on the CO coverage. The transient spectra at saturation coverage consisted of a single peak, whereas at low coverage (0.25 ML) the line shape became asymmetric and each transient peak could be deconvoluted to the multiple components. The origin of the remarkable change in the transient spectral features at the 0.25 ML surface is discussed.

An optical pulse shaping system using a spatial light modulator (SLM) controlled by genetic algorithm (GA) optimization was improved and we demonstrated that the time for finding the optimal condition could be shortened by a proposed “thinning out” method. In this method, GA controls only every N (N=1, 2, 4, 8, 16) pixel in the SLM. The conditions of the remaining pixels are derived by interpolation. The effectiveness of this method was verified by the pulse compression of chirped femtosecond pulses and the increase in the two-photon excitation efficiency of α-perylene crystals. The influence of the thinning out on the pulse shape is discussed, and an advanced method is proposed. It is shown that the disadvantages of the thinning out method can be compensated for by changing the value of N during optimization.

Time-resolved sum-frequency generation spectroscopy was carried out on a deuterated formate (DCOO) adsorbed on Ni(1 1 1) surface to investigate the surface reaction dynamics under instantaneous surface temperature jump induced by the irradiation by picosecond laser pulses. The irradiation of pump pulse (800 nm) caused the rapid intensity decrease of both CD and OCO stretching modes of bridged formate on Ni(1 1 1). Different temporal behaviors of intensity recovery between these two vibrational modes were observed, i.e., CD stretching mode recovered faster than OCO. This is the first result to show that the dynamics of adsorbates on metals strongly depends on the observed vibrational mode. From the results of temperature and pump fluence dependence, we concluded that the observed intensity change was not due to the decomposition or desorption, but was induced by a non-thermal process.

We made the first observation of transient vibrational spectra of both adsorbate and adsorbent at molecule-adsorbed surface using a two-color infrared picosecond laser system. The transient measurements were carried out on the CO-adsorbed surface hydroxyl group (OD) of DM-20 zeolite by pumping the CO stretching mode (2175 cm−1) or OD stretching mode (2470 cm−1) and probing over the CO and OD stretching region (2000–2700 cm−1). The T1 lifetime for OD was 5.8 ps and that for CO was 540 ps. By comparison with other CO-adsorbed systems, vibrational relaxation mechanisms of CO on various surfaces are discussed. We also found evidence of energy flows from the vibrational mode of the adsorbent (OD stretching) to that of the adsorbate (CO stretching) via van der Waals interaction.

Second harmonic generation (SHG) spectroscopy using a tunable femtosecond laser has been demonstrated as an effective and a practical in situ monitor of surface electronic states during adsorption processes. We have successfully shown this technique to be suitable for the study of surface electronic states, not only those induced by adsorbed molecules but also those associated with clean surfaces. By observing the change in the SH signals from a Cu(1 1 1) surface during exposure to benzene or CO molecules, we discovered new resonances of the clean Cu surface that could not be ascribed to the well-known surface state (SS)–image state (IS) transition. One of these was from a surface site that is less likely to adsorb benzene, where the SH signal intensity was kept constant until the Cu surface was covered by the sub-monolayer.

Exchanging of K+ ions existing between layers of a layered photocatalytic compound, K4Nb6O17, with other metal ions changes the catalytic reactivity. Here we report effects of the ion-exchange of part of K+ with Ni2+ or H+. Transient absorption decay due to electron–hole recombination was affected by Ni2+ in the interlayer; faster decay in the picosecond region was observed. The result is consistent with the fact that Ni2+-exchanged K4Nb6O17 shows drastic decrease in photocatalytic reactivity. On the other hand, no difference was observed for the H+-exchanged film when the dacay was compared to that of the original K4Nb6O17, despite the reduction of protons, namely H2 generation, has been observed in photocatalysis. Dynamics of photogenerated electrons in the femto- and picosecond regime is discussed in detail.

The behavior of D2O ice on CO/Pt(1 1 1) and Pt(1 1 1) under the irradiation of near-IR pulses (NIR) was studied by sum-frequency generation (SFG) spectroscopy. The peaks assigned to the O–D stretching modes of ice were obtained for the first 30 molecular layers on Pt(1 1 1). When the D 2 O / CO / Pt (1 1 1) was irradiated, the signal of D2O was weakened after 500 ps, but that of CO was weakened immediately after the pumping. A similar time response was observed for the D2O peak in D 2 O / Pt (1 1 1) . The weakening of SFG is attributed to the broadening of bands due to thermal excitation. This indicates that the energy of the pump pulse is deposited on the Pt(1 1 1) surface and diffused into the layers of D2O ice in the 500 ps timescale.

A UV excitation by a picosecond pulse at 266 nm induced an unusual shoulder on the νCO = 1 ← 0 resonance peak of CO/Ni(111) monitored by sum-frequency generation (SFG) of visible and IR pulses. The observed line shape was reproduced by the use of a dipole-dipole interaction model with the coherent potential approximation (CPA) where the hot band transition with a population ratio of 0.3 to 0.7 (v = 1 to v = 0) was assumed. Neither the transition to the two-phonon bound state nor the coupling with the low-frequency phonon modes explained the observed changes. The shoulder appeared only during the UV excitation, which indicated that the electronically driven excitation, presumably by the hot electrons generated by the irradiation, dominated the process. As possible mechanisms, the involvement of an intermediate negative ion resonance state and/or the non-adiabatic coupling of electronic states with C–O stretching mode were considered.

The transient absorption spectra of OD stretching mode of isobutene-adsorbed hydroxyl groups of DM20 zeolite were measured by picosecond infrared–infrared pump–probe experiment. The vibrational relaxation time ( T 1 ) of the v =1 state was estimated to be 12±2 ps from the temporal profile of the bleaching and hot bands of the OD stretching mode. We found a band indicating the production of a short-lived species at 40 ps after excitation. Moreover we observed the course of isobutene-desorption in the time region from 40 to 100 ps. This result implies that this desorption does not occur immediately but occurs after local vibrational relaxation.

Time-resolved vibrational measurements were carried out on formate (HCOO) adsorbed on Ni(1 1 1) surface by combining the sum-frequency generation method and picosecond laser system (time resolution of 6 ps). Rapid intensity decrease (within the time resolution) followed by intensity recovery (time constant of several tens of ps) of CH stretching signal was observed when picosecond 800 nm pulse was irradiated on the sample surface. From the results of temperature and pump fluence dependences of temporal behaviour of signal intensity, we concluded that the observed intensity change was induced by non-thermal process. Mechanism of the temporal intensity change was discussed.

Two kinds of monolayered films of ion-paired macrocyclic amphiphiles formed from anionic surfactant 1,2-bis[(dodecyloxy)carbonyl]ethane-1-sulfonate and tetracationic macrocycles with different molecular sizes were prepared on hydrophilic silica plates by the Langmuir−Blodgett technique. Vibrational sum-frequency generation (SFG) spectroscopy was applied to investigate the packing structure of the alkyl chains of the films. The SF intensity ratio of the CH symmetric stretching mode of the methylene group to that of methyl group in the alkyl chains increased when the occupied area of the macrocycle was larger than the sum of the cross-sectional areas of the hydrophobic alkyl tails. The appearance of a methylene CH band in the SFG spectra implies the presence of gauche conformation in the alkyl chains. This indicates that the molecular size of the cyclic tetracation hydrophilic head exclusively governs the packing structure of the alkyl group hydrophobic tails in the monolayer state. The results show that mo...

Transient absorption spectra of the layered compound K4Nb6O17, which is known as a photocatalyst for splitting water into H2 and O2, were measured by the femtosecond UV pump and visible probe technique. Under band-gap excitation of a K4Nb6O17 single crystal and a spin-coated K4Nb6O17 film, a broad transient absorption extending over the whole visible region, which could be ascribed to photogenerated carriers in K4Nb6O17, was observed, and its decay behavior was analyzed on the basis of second-order kinetics. Dynamics of photoexcited Ru(bpy)32+ intercalated at K4Nb6O17 interlayers was also investigated. Intercalation of Ru(bpy)32+ in K4Nb6O17 is known to give visible light response for photocatalytic chemical reaction. Observed transient bleaching of Ru(bpy)32+ band showed fast and nonexponential decay differing from that of Ru(bpy)32+ in water. The decay mechanism is discussed in terms of electron transfer between Ru(bpy)32+ and K4Nb6O17.

Spectral and kinetic behavior of thermal cis-to-trans isomerization of 4-aminoazobenzene (AAB) is examined in various solvents of different polarities. In contrast to azobenzene (AB), it is found the rate of thermal isomerization of AAB is highly dependent on solvent polarity. Accelerated rates are observed in polar solvents as compared to nonpolar solvents. Moreover, a decrease in the barrier height with an increase in medium polarity is observed. Our observations suggest that inversion is the preferred pathway in cis-to-trans thermal isomerization in a nonpolar medium; however, in a polar medium, the isomerization path deviates from the inversion route and rotational behavior is incorporated. Differences in the kinetics and in mechanisms of isomerization in different media are rationalized in terms of modulation in barrier height by polarity of the medium and solute-solvent interaction. It is found that kinetics as well as the mechanism of thermal isomerization in AAB is controlled by the polarity of the medium.

Picosecond infrared-infrared pump−probe experiments in the OD stretching region were carried out on dehydrated and multilayer water-adsorbed γ-Al2O3. For the dehydrated γ-Al2O3, transient bands assigned to the bleaching and hot bands of the OD stretching mode of isolated surface hydroxyl groups were observed, and the population lifetime (T1) of the vibrational excited state (v = 1) of the mode was 200 ± 10 ps at 293 K. The characteristic temperature dependence of T1 is indicative of a seven-phonon process. For the water-adsorbed γ-Al2O3, the transient bleaching and transient hot bands with a lifetime of 10−12 ps were observed by excitation of the absorption peak at 2630 cm-1. In addition to these bands, weak transient bands were observed in the low-frequency region. These results are considered evidence of the existence of isolated water molecules on the γ-Al2O3 surface. Pure dephasing is also discussed based on the bandwidth of the observed transient bands.

Sum-frequency generation (SFG) spectroscopy was applied to the study of plasma hydrogenated diamond C(100) surface of a synthetic diamond. Two vibrational resonance peaks with the intensities strongly dependent on the polarization combinations of the visible and infrared beams were observed at 2899 and 2924 cm−1. From the results of SFG measurements for various polarization combinations, the 2899 and 2924 cm−1 peaks were assigned, respectively, to the antisymmetric and symmetric CH stretching modes of HCCH group on H/C(100)-2×1 surface. In addition, a strong background signal with an oscillatory profile was observed.

Vibrational study by Raman spectroscopy was made of the layered perovskite compounds of the formula M2La2Ti3O10 (M = H, Li, Na, K, Rb), K2La2Ti3O10·2H2O, and H2La2Ti3O10·nH2O. The spectral features above 400 cm-1 were similar in all of the unhydrated samples suggesting that the bands originated from the vibrational modes of the La2Ti3O10 perovskite layer. Lattice dynamical calculations were performed with the use of a potential field derived from the molecular dynamics on the M2La2Ti3O10 (M = Li, Na, K). The assignment of the Raman bands higher than 400 cm-1 was made on the basis of the results of lattice dynamical calculations and was confirmed by comparing the spectral feature of K2La2Ti3O10 with that of H2La2Ti3O10, K2La2Ti3O10·2H2O, and H2La2Ti3O10·nH2O.

The combination of an instantaneous temperature jump induced by the irradiation of picosecond laser pulses and the subsequent observation by sum-frequency generation spectroscopy enabled the identification of a short-lived reactive intermediate in the decomposition of formate on NiO(111) surface. The irradiation of 1064 nm laser pulses caused the vibrational peak at 2160 cm−1, which is the CD stretching mode νCD of bidentate formate, to weaken and the νCD of monodentate formate at 2190 cm−1 to appear. The spectral changes recovered in 100 ps time scale but not fully above 400 K. The observations suggested that the formate in bidentate configuration transformed to monodentate formate prior to decomposition. Temperature- and time-dependent features indicated that the two types of formate were in equilibrium and the equilibrium shifted towards the monodentate form by a rapid laser-induced temperature jump of about 250–300 K. The experiment enabled us to identify short-lived species and to estimate kinetic parameters. The enthalpy difference between bidentate and monodentate formates and the activation energy for the decomposition of monodentate formate were 19±5 and 30±10 kJ/mol, respectively.

A spectroscopic study of adsorbed CO on Ni(111) was carried out using infrared-visible sum-frequency generation (SFG) and infrared reflection absorption spectroscopy (IRAS). An anomalous coverage-dependence of the SFG signal intensities of bridged and linear CO was found. While the SFG signal of bridged CO at 1920 cm -1 gained intensity with increasing CO coverage in the region between 0 and 0.4 ML ( 1 monolayer, ML: saturation coverage at 130 K), it weakened and disappeared when linear CO (2074 cm -1 ) was present on the surface above 0.47 ML. The IRA peak of bridged CO, however, did not disappear at the increased coverage suggesting that the weakening of the SFG signal of bridged CO is not caused by the decrease in the coverage but by the suppression of the SFG process of bridged CO by the coexistence of linear CO. The spectra of isotope mixtures of C 16 O and C 18 O clearly indicated that the weakening of SFG signals is not caused by the dipole-dipole coupling between the vibrational modes of bridged and linear CO. The anomalous coverage-dependence of the SFG signal was ascribed to the change of the Raman tensor by the coadsorption of linear CO.

The effects of irradiation by picosecond ultraviolet (266 nm) and visible (532 nm) pulses of CO-covered Ni(111) and NiO(111)/Ni(111) surfaces were investigated by infrared-visible sum-frequency generation (SFG) spectroscopy. As a result of the irradiation of UV pulses, the SFG signal by the v =1←0 bands of the CO stretching mode weakened and transient peaks tentatively assigned to the v =2←1 hot band transition appeared with a downshift by 18 and 14 cm −1 from v =1←0 bands on the metal and oxide-layered surfaces, respectively. The time profile of the weakening and that of the transient signal were coincident with the same rise and fall times of less than ∼10 ps. The irradiation of visible pulses also induced a weakening of the v =1←0 bands and transient peaks, but the decay time on the metal surface was longer than 100 ps. The temporal and spectral features imply that the persistent v =1←0 band and the transient band originated from the same CO molecule. Short decay times observed on irradiating UV pulses on to the Ni(111) and NiO(111) surfaces and that of the visible pulses on to the NiO(111) surface suggest that the photo-generated hot electrons induced the observed spectral changes. The long decay time observed on irradiating visible pulses on to the Ni(111) surface suggests the occurrence of a thermally driven process. Participation of the negative ion state was considered to be one of the possible mechanisms for the rapidly decaying features.

We succeeded in identifying the intermediates in thermal decomposition reactions by utilizing the combination of an instantaneous temperature jump induced by the irradiation of picosecond laser pulses and the subsequent observation by time-resolved sum-frequency generation (TR-SFG) spectroscopy. The short-lived reactive intermediates in the decomposition of formate on NiO(111) and Ni(111) surfaces were identified. The irradiation of 1064 nm laser pulses caused the vibrational peak of the CD stretching mode ν CD of bidentate formate on NiO(111) to weaken and the ν CD band of monodentate formate to appear. The result on Ni(111) showed the weakening of the ν CD band of bridging formate and the appearance of the CO stretching mode ν CO of monodentate formate. The spectral changes recovered on a 100 ps time scale but not fully above 400 K for the NiO(111) system and 320 K for the Ni(111) system, indicating the onset of thermal decomposition in the high-temperature period. The observations suggested that the formate in the stable bidentate/bridging configurations transformed to unstable monodentate formate prior to decomposition. Temperature- and time-dependent features indicated that the two types of formate were in equilibrium and the equilibrium shifted towards the monodentate form by the rapid laser-induced temperature jump of about 250–300 K.

By means of infrared pump-probe technique, spectroscopic feature of vibrationally excited water molecule (D2O) on mordenite zeolite (OD) has been investigated. Populational lifetime of the OD stretching band (ν3:2730cm-1) was determined to be 43±5 ps at 123 K by the time evolution of hot band. The transient bleachings and absorptions appeared when the D2O molecule was promoted to the vibrationally excited level of the OD stretching modes. Especially, the transient absorption at 2680 cm-1 has rapid decay time (≈15 ps) and it was assigned as the overtone between ν3 mode and vibrationally excited ν1 mode (2620 cm-1).

The vibrational relaxation lifetimes of the CO stretching mode of Cr(CO)6 and Mo(CO)6 adsorbed in the cage of the HY, DY and NaY-type zeolites were measured at various temperature by pump-probe method using picosecond infrared laser pulses. It was shown by comparing the lifetimes that the accepting modes include both the vibrational modes of the metal carbonyl and those associated with the cations on the zeolite surface. The analysis of the temperature dependence of the lifetimes revealed that the number of the excited accepting modes are four with their energy lying around 500 cm-1.

Experiments have been carried out on propionate and formate adsorbed on clean and regulatively oxidized Ni(100) surfaces to scrutinize the notion that the polarization characteristics of infrared-visible sum frequency generation (SFG) signals of molecules on metallic surfaces are different from those due to molecules on insulating surfaces. Both propionate and formate give signals only for p-polarized visible pulses on clean metal and oxygen-saturated surfaces, but signals due to s-polarized visible pulses appeared from the propionate-covered surface as soon as the surface was covered with a monolayer of NiO(100). Vibrational peaks of propionate were located at 2887, 2945, and 2988 cm−1 and were assigned to the symmetric stretching mode of CH2 group, the symmetric stretching mode of CH3 group, and the degenerate stretching mode of CH3 group, respectively. The peak of the surface formate was located at 2948 cm−1 on the clean metal surface, but another band appeared at 2860 cm−1 on oxide-layered surfaces. The causes of the appearance of the (sp) polarization signals by the presence of the NiO layer are discussed.

Spectroscopic and dynamic features of the vibrationally excited D2O/zeolite system have been investigated by two-color infrared–infrared pump–probe experiment. The frequency- and delay-scanned probe intensities were measured by tuning the pump laser to the OD stretching bands of the D2O molecule hydrogen bonded to the acidic OD group of mordenite zeolite. Two types of pump-induced signals were observed: the ones which have the population lifetime of 43±5 ps and display frequency shift by the pumping frequency, and the others, which have the lifetime of about 15 ps and exhibit no such frequency shift. Possible origins of the signals are discussed.