Measurement time-resolved resonance Raman

Aramaki and Atkinson were also active in work on the spiro-oxazines [65]. They noted that for NOSH in many polar and nonpolar solvents the picosecond time-resolved resonance Raman spectra simply built up over 50 psec with no shape evolution. The same finding was concluded from transient absorption measurements over the same time scale. The spectra/absorbances were then constant for 1.5 nsec. These authors suggest that only two isomers can be expected to contribute to the merocyanine spectra because those trans about the y-methene bridge bond attached to the naphthalene ring are sterically crowded due to short interproton distances. There was no evidence for the X transient in their study however, the 50-psec convoluted pulse profile may be expected to mask this sortlifetime species even if it were present. 

When an electron is injected into a polar solvent such as water or alcohols, the electron is solvated and forms so-called the solvated electron. This solvated electron is considered the most basic anionic species in solutions and it has been extensively studied by variety of experimental and theoretical methods. Especially, the solvated electron in water (the hydrated electron) has been attracting much interest in wide fields because of its fundamental importance. It is well-known that the solvated electron in water exhibits a very broad absorption band peaked around 720 nm. This broad absorption is mainly attributed to the s- p transition of the electron in a solvent cavity. Recently, we measured picosecond time-resolved Raman scattering from water under the resonance condition with the s- p transition of the solvated electron, and found that strong transient Raman bands appeared in accordance with the generation of the solvated electron [1]. It was concluded that the observed transient Raman scattering was due to the water molecules that directly interact with the electron in the first solvation shell. Similar results were also obtained by a nanosecond Raman study [2]. This finding implies that we are now able to study the solvated electron by using vibrational spectroscopy. In this paper, we describe new information about the ultrafast dynamics of the solvated electron in water, which are obtained by time-resolved resonance Raman spectroscopy. 

A variety of spectroscopic methods has been used to determine the nature of the MLCT excited state in the /ac-XRe(CO)3L system. Time-resolved resonance Raman measurements of /ac-XRe(CO)3(bpy) (X = Cl or Br) have provided clear support for the Re -a- n (bpy) assignment of the lowest energy excited state [44], Intense excited-state Raman lines have been observed that are associated with the radical anion of bpy, and the amount of charge transferred from Re to bpy in the lowest energy excited state has been estimated to be 0.84 [45], Fast time-resolved infrared spectroscopy has been used to obtain the vibrational spectrum of the electronically excited states of/ac-ClRe(CO)3(bpy) and the closely related/ac-XRe(CO)3 (4,4 -bpy)2 (X = Cl or Br) complexes. In each... 

The use of picosecond pulses to minimize the Interference of fluorescence with the Raman spectrum was also demonstrated (5) at about that time. The use of vldicon detection in Raman spectroscopy was demonstrated (6) in 1976. The first resonance Raman spectrum taken for a photobiologlcal system (bacteriorhodopsin) in the nanosecond time scale was (7) in 1977. The resonance Raman spectra of bacteriorhodopsin have also been measured in the microsecond (8,9,10) and in the millisecond (11) time domain. Recently the time resolved resonance Raman spectra of photolyzed hemoglobin derivatives have been reported (12). 

RISC has also been observed by a two-color method for the isoalloxazine structures 59-62 shown in Chart 2 [39]. The discovery of RISC in these compounds came about as a result of time-resolved resonance Raman measurements on their triplet states. fluorescence generated by the Raman probe pulse... 

The properties of both mentioned carbenes have been studied in detail by means of time-resolved resonance Raman spectroscopy and density functional calculations [58]. The measured spectra confirmed the triplet character... 

The effect of oxygen on cyclic 1,3-diradicals shows that conformation can affect the triplet state lifetime ST Time resolved resonance Raman spectroscopy has been used to examine triplet states produced from different isomers of p-carotene. A theoretical study has also been reported on the a-cleavage of the triplet states of symmetric and non-symmetric ketones S mechanism for triplet state relaxation of aromatic molecules has been used to explain experimental data for substituted benzenes. The decay kinetics of triplet-triplet fluorescence in the mesitylene biradical (two sub-levels) have been measured between 10 and 77K in Shpolski matrices triplet state of dimesityl... 

The following is an excellent example where a special technique, in this case time-resolved resonance Raman spectroscopy added significant information which simple optical absorption measurements could not provide. The system of interest is aniline and its radicals generated upon oxidation (e.g., by N3 ). The latter are the radical cation and its deprotonated form existing in equilibrium 12 with a pK of 7.04.29... 

Time-resolved resonance Raman spectroscopy was used to follow photochemical transformations of OCIO. Similar measurements gave information on environment-dependent photophysics of CIO2 in the Bi- A2 electronic transi-tion. Absolute Raman intensities were reported for OCIO dissolved in chloro-form. ... 

In essence, two of these three electrons form a n bond, on top of the existing (j bond, and the remaining electron is place into an antibonding n orbital. The sulfur-sulfur bond thus assumes a partial 7c-character 1112,113]. As a direct consequence, the rotation becomes restricted and, particularly in cyclic disulfides, molecular structures may flatten. Even the possible formation of cis- and rran -isomers of (MeSSMe) could recently be verified through identification of two distinct vibrational stretching frequencies evaluated from time-resolved resonance Raman spectroscopy measurements. These findings were also supported by corresponding calculations [118, 119, 146]. 

Recent advances in time-resolved vibrational spectroscopy (time-resolved infrared [TR-IR] and time-resolved resonance raman spectroscopy) have provided further evidence for the description of aryl nitrenium ions as imino-cyclohexadienyl cations. The C-N stretching frequency in singlet diphenylni-trenium ion (generated by LFP of a N-diphenylaminopyridinium salt in acetonitrile) was measured by time-resolved infrared spectroscopy to be v = 1392 cm , which is significantly higher than the v = 1320 cm of diphenylamine. In the UVA is, the diphenylnitrenium ion shows = 425 and 660 nm, with a lifetime X = 1.5 Rs. ... 

Various possible time resolved techniques are discussed which enable one to measure the vibrational spectra (and what they entail of structural information) of the distinct transient intermediates formed in different photochemical decomposition schemes and at different times (in the sec-picosec range). The techniques make use of 1) the difference in the time development behavior of the different intermediates, 2) the difference in the absorption maxima and thus the difference in the resonance Raman enhancements for the different intermediates, and 3) the laser power. The techniques use one or two lasers for the photolytic and probe sources as well as an optical multichannel analyzer as a detector. Some of the results are shown for the intermediates in the photosynthetic cycle of bacteriorhodopsin. 

CLM method can also be combined with various kinds of spectroscopic methods. Fluorescence lifetime of an interfacially adsorbed zinc-tetra-phenylporphyrin complex was observed by a nanosecond time-resolved laser induced fluorescence method [25]. Microscopic resonance Raman spectrometry was also combined with the CLM. This combination was highly advantageous to measure the concentration profile at the interface and a bulk phase [14]. Furthermore, circular dichroic spectra of the liquid-liquid interface in the CLM could be measured [19]. 

Thus far, the only excited-state structural dynamics of oligonucleotides have come from time-resolved spectroscopy. Very recently, Schreier, et al. [182] have used ultrafast time-resolved infrared (IR) spectroscopy to directly measure the formation of the cyclobutyl photodimer in a (dT)18 oligonucleotide. They found that the formation of the photodimer occurs in 1 picosecond after ultraviolet excitation, consistent with the excited-state structural dynamics derived from the resonance Raman intensities. They conclude that the excited-state reaction is essentially barrierless, but only for those bases with the correct conformational alignment to form the photoproducts. They also conclude that the low quantum yields observed for the photodimer are simply the result of a ground-state population which consists of very few oligonucleotides in the correct alignment to form the photoproducts. 

The determination of excited-state structural dynamics in nucleic acids and their components is still in its infancy. Although progress has been made in understanding the excited-state structural dynamics of the nucleobases, primarily with UV resonance Raman spectroscopy, much work still remains to be done at that level to be able to extract the structural determinants of the excited-state structural dynamics and resulting photochemistry. Much less is known about the excited-state structural dynamics of nucleotides, oligonucleotides, and nucleic acids, but the static and time-resolved spectroscopic tools exist to be able to measure them. 

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