Spectroscopy, action

The temi action spectroscopy refers to how a particular action , or process, depends on photon energy. For example, the photodissociation of 0 with UV light leads to energetic 0+0 fragments the kinetic energy released has been... 

The temi action spectroscopy refers to those teclmiques that do not directly measure die absorption, but rather the consequence of photoabsorption. That is, there is some measurable change associated with the absorption process. There are several well known examples, such as photoionization spectroscopy [47], multi-photon ionization spectroscopy [48], photoacoustic spectroscopy [49], photoelectron spectroscopy [, 51], vibrational predissociation spectroscopy [ ] and optothemial spectroscopy [53, M]. These teclmiques have all been applied to vibrational spectroscopy, but only the last one will be discussed here. 

He2 ICl conformer using action spectroscopy to find the bound-free continuum associated with the He + He IC1(B, V = 3) dissociation limit. It would also be insightful to perform time-resolved experiments on the different conformers of these systems to directly monitor the kinetics for forming the different products and intermediates as a function of the different excited-state levels prepared. 

Redlight pretreatment decreases the phototropic sensitivity for the first positive curvature by a factor of 10. Con and Briggs37) demonstrated by action spectroscopy that this decrease is mediated by phytochrome. It appears that there is an interaction... 

Among the many sensory reactions Phycomyces displays, the study of the photoreceptor and adaptation deserves maximal attention, since Phycomyces shares these two attributes with a variety of other blue light sensitive organisms. Action-spectroscopy indicates a flavin as the photoreceptor of Phycomyces. /3-carotene was positively ruled out as a possible receptor, since mutants with no trace amounts of )3-carotene are phototropical normal. The photoreceptor has not yet been isolated. As in other systems the difficulty consists in distinguishing the flavin photoreceptor from the bulk flavoproteins in the cell. One therefore needs unambiguous criteria for the identification of the photoreceptor. The most promising approach for an isolation would be a photoreceptor mutant and we described the properties those mutants should have. Until now there is no firm evidence that the photomutants, madA or madB are defective in the photoreceptor. 

Infrared spectroscopy is the workhorse in this field, because it can quickly provide dynamical details, discriminate between different cluster sizes and phases [40], and sample a wide spectral range. It often yields valuable feedback for quantum chemical calculations. In contrast to some action spectroscopy techniques, IR absorption spectroscopy is not intrinsically size-selective. All cluster sizes generated in the expansion are observed together, and indirect methods of size assignment are needed. 

Hartman KM. Action spectroscopy. In Lohmann W, Marke H, Ziegler H, eds. Biophysics. Heidelberg Spinger-Verlag, 1983 115. 

Lipson ED. Action spectroscopy methodology. In Horspool WH, Song P-S, eds. Handbook of Organic Chemistry and Photobiology. Boca Raton, FL CRC Press, 1995 1257. 

Sineshchekov and coworkers could show the direct involvement of both proteins in photoperception (50, 63). Action spectroscopy with knock-down mutants revealed a maximum sensitivity for ChRl at 500 and 470 nm for ChR2. Photophobic responses were impaired by reduction in ChR content while the involvement in phototaxis is still unclear. Chlamydomonas rhodopsins are light-gated ion channels. While the highest conductance is for H -ions the conductance for calcium plays the dominant role under physiological conditions. 

As mentioned in Section 9.2, there is an important distinction between action spectroscopies based on the absorption of multiple photons, as is possible with FEL excitation, and those based on single photon absorption, such as messenger spectroscopy [26,27], laser-induced reaction spectroscopy [73] or indeed direct absorption experiments. When the signal (in this case, the depletion of the parent ion and creation of product ious) depends on the absorption of multiple photons, the signal intensity may not be compared directly to computed linear (single-photon) absorption spectra, as is the normal fashion. There are several reasons why intensities may differ. Thus, baudpositiou (frequency) is considered usually to be more reliable than band intensity when comparing computed and experimentally-measured spectra. 

UV/visible PD action spectroscopy is currently not as popular as IR action spectroscopy and, to date, has yielded relatively little structural information on... 

Photo-excitation of gas-phase ions may result in the photodetachment of an electron rather than photo-fragmentation. Coulombic considerations dictate that this process is more prevalent for anions than for cations. Electron photodetachment action spectroscopy of trapped anions has proved also to be a valuable source of molecular information. In some systems, electron photodetachment and PD compete. The mechanisms for these two processes in large molecules are yet to be understood fully consequently, their branching ratios in specific experimental conditions cannot be predicted as yet. One exciting possibility is the idea of using frequency and phase-shaped pulses to promote selected photochemical pathways. 

Bush, M.F. Oomens, J. Saykally, R.J. Williams, E.R. Effects of alkaline earth metal ion complexation on amino acid zwitterion stahihty Results from infrared action spectroscopy. J. Am. Chem. Soc. 2008,130, 6463-6471. 

McQueen, P.D. Jockusch, R.A., Visible action spectroscopy and fluorescence of gas-phase fluorescein. In preparation. 

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