Spectroscopy time domain/resolved

Time-domain Raman measurement of molecular submonolayers by time-resolved reflection spectroscopy. /. Phys. Chem. B, 108, 1525-1528. 

Strand cleavage studies have provided relative rate constants for hole transport versus the rate constant for the initial chemical event leading to strand cleavage [18-20]. However, they do not provide absolute rate constants for hole transport processes. Several years ago we introduced a method based on femtosecond time-resolved transient-absorption spectroscopy for investigating the dynamics of charge separation and charge recombination in synthetic DNA hairpins [21, 22]. Recently, we have found that extensions of this method into the nanosecond and microsecond time domains permit investigation of the dynamics of hole transport from a primary hole... 

Beyond imaging, the combination of CRS microscopy with spectroscopic techniques has been used to obtain the full wealth of the chemical and the physical structure information of submicron-sized samples. In the frequency domain, multiplex CRS microspectroscopy allows the chemical identification of molecules on the basis of their characteristic Raman spectra and the extraction of their physical properties, e.g., their thermodynamic state. In the time domain, time-resolved CRS microscopy allows the recording of the localized Raman free induction decay occurring on the femtosecond and picosecond time scales. CRS correlation spectroscopy can probe three-dimensional diffusion dynamics with chemical selectivity. 

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). 

The experimental techniques adopted to measure linear and nonlinear optical properties are quite different and must be discussed separately. In broad terms, linear properties can be measured using low intensity probes and high spectral resolution. They are usually understood in the frequency domain. Nonlinear responses on the contrary need very large intensities, typically achieved in short pulses, and are discussed in the time domain. In addition to these physical considerations, we have to remember that time-resolved spectroscopy and optical characterization usually require good optical quality samples, so our understanding of the physics of these materials is closely linked to their quality. 

Recent laser flash photolysis studies of the kinetics of the process 7 —> 9 suggest that following photoexcitation with time-resolved spectroscopy, an isomer 8 (E form) is formed in the nanosecond or microsecond time domain which undergoes a first-order conversion to the Z form 9.42 43 Details will be published elsewhere. 

Vibrational spectroscopy has proven to be a powerful method of studying biological molecules. Continued technical improvement (FT spectroscopy, time resolved spectroscopy, etc.) open up new domains of investigation which help solve fundamental problems of structure-function correlation at the molecular level. Many domains are beginning to be explored, and results are expected in the fields of compatible biomaterials, intelligent drug development, and in vivo spectroscopic measurement. 

Time resolved coherent anti-Stokes Raman spectroscopy of condensed matter has been recently extended to the femtosecond domain allowing direct and detailed studies of the fast relaxation processes of molecular vibrations in liquids. The vibrational phase relaxation (dephasing) is a fundamental physical process of molecular dynamics and has attracted considerable attention. Both experimental and theoretical studies have been performed to understand microscopic processes of vibrational dephasing. Developments in ultrafast coherent spectroscopy enables one now to obtain direct time-domain information on molecular vibrational dynamics. Femtosecond time-resolved coherent anti-Stokes Raman scattering measuring systems have been constructed (see Sec. 3.6.2.2.3) with an overall time resolution of less than 100 fs (10 s). Pioneering work has been per-... 

Parent radical cations derived from alkanes and alkyl chlorides can be directly observed in the nanosecond time domain by time-resolved spectroscopy such as laser flash photolysis and electron pulse radiolysis. Especially the latter one enables the direct ionization of the solvents independently on the optical properties of the sample and a well-defined electron transfer regime according to Eq. (2) or (3). Representative examples of the radiolyfic generation of solvent radical cations are given in Eqs. (4) and (5a) for the cases of 1-chlorobutane and -decane. ... 

In picosecond time-resolved Raman spectroscopy, the sample is pumped and probed by energetically well-defined optical pulses, producing a full vibrational spectrum over a 1000 2000 cm 1 window.207 One would expect vibrational spectroscopy to be restricted to the picosecond time domain and above by the Heisenberg uncertainty principle (Equation 2.1), because a 1 ps transform-limited pulse has an energy width of... 

Conventional kinetics is largely concerned with the description of dynamic processes in the time domain, and in consequence few conceptual problems are encountered in understanding time resolved experiments. By contrast, frequency resolved measurements often pose more of a challenge to understanding, in spite of the obvious correspondence between the time and frequency domains. This conceptual difficulty may explain why the only frequency resolved method to achieve universal acceptance in electrochemistry is electrochemical impedance spectroscopy (EIS) [27-29], which analyses the response of electrochemical systems to periodic (sinusoidal) perturbations of voltage or current. It is clear that EIS is a very powerful method, and there... 

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