Jump resolved spectroscopy

Time-resolved spectroscopy is performed using a pump-probe method in which a short-pulsed laser is used to initiate a T-jump and a mid-IR probe laser is used to monitor the transient IR absorbance in the sample. A schematic of the entire instrument is shown in Fig. 17.4. For clarity, only key components are shown. In the description that follows, only those components will be described. A continuous-wave (CW) lead-salt (PbSe) diode laser (output power <1 mW) tuned to a specific vibrational mode of the RNA molecule probes the transient absorbance of the sample. The linewidth of the probe laser is quite narrow (<0.5 cm-1) and sets the spectral resolution of the time-resolved experiments. The divergent output of the diode laser is collected and collimated by a gold coated off-axis... 

Yamakata, A., Uchida, T., Kubota, J. and Osawa, M. (2006) Laser-induced potential jump at the electrochemical interface probed by picosecond time-resolved surface-enhanced infrared absorption spectroscopy./. Phys. Chem. B, 110, 6423-6427. 

Fig. 2. a) Required number of incoming x-ray photons to observe time-resolved EXAFS of transition metal compounds in H20 solution with a signal-to-noise ratio S/N = 1. No ligand or counterion contributions were included (see Fig. 1). Input parameters are /= 10%, %= 1 % (relative to the absorption edge jump of the selected element). The maxima of curves 2) in Fig. 1 for Fe and Ru correspond to the data points for these elements, b) Feasibility range for time-resolved x-ray absorption spectroscopy. The shaded region indicates the required x-ray dose per data point as a function of the fraction of activated species for the calculated EXAFS experiments on transition metal compounds shown in a). Curves (1) to (3) are extrapolated from experimental results (see section 3. for details) of time-resolved XANES.

Perturbation or difference experiments provide another method for simplifying the data in both Raman and IR experiments. The classic approach is to introduce isotopic substitutions which identify the chemical groups responsible for the vibration and permit vibrational normal mode assignments. Chemical modification of the prosthetic group or of the protein and amino acid mutation are additional possibilities. Temperature jump, pressure jump, and rapid mixing experiments are also valuable approaches. This introduction emphasizes the use of time-resolved vibrational spectroscopy to examine the vibrational information selectively. It is not possible in this chapter to describe all of the possible ways to study biological systems using vibrational spectroscopy. Examples of the use of resonance Raman spectroscopy to study the structure and... 

An acetyl and an amide group block the N and C termini of the peptide chain. The tryptophan residue is added as a probe to collect time-resolved fluorescence signal under nanosecond T-jump spectroscopy, allowing measurement of coil to helix transition. The experimentally estimated relaxation time at room temperature for this transition is about 300 ns. The inverse of the experimental relaxation time is the sum of two rate constants, from the unfolded to the folded state and back. The equilibrium constant of this transition is about 1, which indicates that the forward and the backward rates are almost the same. The experimental first passage time from the folded to the unfolded state (which we estimate computationally in this chapter) is therefore 600 ns. This timescale seems achievable within the standard model and atomically detailed simulations. However, one should keep in mind that an ensemble of trajectories is required to study kinetics. The calculation of kinetics will be at least 100 times more expensive than the calculation of a single trajectory and therefore difficult to do with the usual standard model. 

A new method for measuring diffusion coefficients by IR spectroscopy was developed by Karge and Niessen [158],Niessen [132] and Karge et al. [939]. The change in the intensities of bands typical of molecules migrating inside a zeolite structure during their uptake or desorption were measured by FTIR spectroscopy under high time-resolution as a fimction of small partial pressure jumps and at various temperatures. An appropriate method of evaluation of the time-resolved spectra was developed on the basis of solutions of Fick s second diffusion law provided by Crank [940]. As an example,Fig. 53 illustrates an uptake experiment with benzene (B) as the adsorbate and H-ZSM-5 as the adsorbent. 

Time-resolved FTIR spectroscopy measurements were performed under isothermal crystallisation conditions to clarify the origin of the cocrystallisation and phase segregation phenomena observed for a series of PE blends between the deuterated and hydrogenated species, The degree of undercooling or the temperature jump depth (i.e., the size of the temperature drop) from the molten state to the isothermal crystallisation temperature was controlled (96). 

H. Lemetyinen, J. Andreasson, and many others have studied other large x-systems including the Cgo molecule. After excitation, electrons or excitations can be seen in time-resolved transient spectroscopy jumping between the connected molecules. This type of work is useful in understanding natural photosynthetic processes. It deserves to be mentioned that ET or conductivity cannot occur without excitation. 

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