Flash photolysis nanosecond

Porter G and Topp M R 1968 Nanosecond flash photolysis and the absorption spectra of excited singlet states Nature 220 1228-9... 

Lewis J W, Yee G G and Kliger D S 1987 Implementation of an optical multichannel analyzer controller for nanosecond flash photolysis measurements Rev. Sol. Instrum. 58 939-44... 

Nanosecond flash photolysis studies of Ct-nitronaphthalene in polar and nonpolar solvents led to the detection of the trip let-triplet absorption spectrum of this nitrocompd (Ref 26). 

Capellos and Suryanarayanan (Ref 28) described a ruby laser nanosecond flash photolysis system to study the chemical reactivity of electrically excited state of aromatic nitrocompds. The system was capable of recording absorption spectra of transient species with half-lives in the range of 20 nanoseconds (20 x lO sec) to 1 millisecond (1 O 3sec). Kinetic data pertaining to the lifetime of electronically excited states could be recorded by following the transient absorption as a function of time. Preliminary data on the spectroscopic and kinetic behavior of 1,4-dinitronaphthalene triplet excited state were obtained with this equipment... 

Nanosecond flash photolysis of 1,4-dinitro-naphthalene in aerated and deaerated solvents showed a transient species with absorption maximum at 545nm. The maximum of the transient absorption was independent of solvent polarity and its lifetime seemed to be a function of the hydrogen donor efficiency of the solvent. The transient absorption was attributed to the lowest excited triplet state of 1,4-dinitronaphthalene. Based on spectroscopic and kinetic evidence, the triplet state of 1,4-dinitronaphthalene behaved as an n - Tt state in nonpolar solvents,... 

Some further information on this system has been obtained by nanosecond flash photolysis. These data are shown in Table 3.4/14b,21) By using... 

Evidence from nanosecond flash photolysis studies indicates that an oxa-ziridine precursor to the diazoketone is unlikely. Photoelimination of nitrogen is also observed in 4-methyl-1,2,3-benzotriazine 3-oxide and affords 3-methylanthranil a mechanism involving loss of nitrogen from an intermediate oxaziridine has been proposed.74... 

The electronic devices used in nanosecond flash photolysis are at the limit of their time responses to the signals they receive. In order to investigate reactions occurring in the sub-nanosecond timescale it is necessary to overcome this problem. 

Figure 1 Differential absorption spectrum obtained upon nanosecond flash photolysis (532 nm) of 7.2 X 10M solutions of Fc-ZnP-H2P-C6o triad in nitrogen saturated benzonitrile with a time delay of 50 nsec at 298 K. (From Ref. 47.)...

C. Capellos, Nanosecond Flash Photolysis of Triphenylamine Solutions , PATR 4439 (1973) 21) C. Capellos K. Suryanarayanan,... 

A Ruby Laser Nanosecond Flash Photolysis System, 1,4-Dinitronaphthalene , PATR 4445... 

Photoisomerizations of cycloheptenes and cyclohexenes are known as well, and photosensitized excitation and isomerization of these have been directly detected using nanosecond flash photolysis techniques19 and time-resolved photoacoustic calorimetry20. 

Recent studies by Schuster and collaborators67,54, based on nanosecond laser flash techniques, revealed important conclusions, including (a). The enone excited state responsible for the photocycloaddition is the jt-Tt which possesses different polarization than the n-7T state, considered in rationalizing the effect of the oriented jr-complex. (b) Direct measurement of the reactivity scale of alkenes measured by nanosecond flash photolysis provided different results from those obtained with no consideration of the diradical fragmentation to starting materials. 

Fig. 9.31 a Differential absorption spectra (visible and near-infrared) obtained upon nanosecond flash photolysis (355 nm) of 17c (2.0 x 10 6 M) in nitrogen-saturated oDCB solutions with a time delay of 100 ns at room temperature, indicating the radical ion pair state features at 680 and 1010 nm. b Time-absorption profiles of the spectra shown above at 1010 nm to monitor the decay of the radical ion pair state... 

The mechanism of 3-haloaniline phototransformation was investigated in more detail in a nanosecond flash photolysis and product analysis study in methanolic solution [52], Photosolvolysis, as witnessed by the formation of anisidine, was again the major pathway, in particular for 3-fluoroaniline. A photoreductive pathway yielding aniline was also observed, being most important for 3-bromoaniline transient absorption indicated the formation of anilino radicals by singlet state dehalogenation as an intermediate on this pathway. Homolytic C - Br cleavage was additionally evidenced. The possibility to observe the triplet-triplet absorption spectra of 3-fluoro- and 3-chloroaniline pointed to an unreactive triplet state [52]. 

Figure 8. (a) Differential transient absorption spectrum obtained upon nanosecond flash photolysis... 

Transient intermediates are most commonly observed by their absorption (transient absorption spectroscopy see ref. 185 for a compilation of absorption spectra of transient species). Various other methods for creating detectable amounts of reactive intermediates such as stopped flow, pulse radiolysis, temperature or pressure jump have been invented and novel, more informative, techniques for the detection and identification of reactive intermediates have been added, in particular EPR, IR and Raman spectroscopy (Section 3.8), mass spectrometry, electron microscopy and X-ray diffraction. The technique used for detection need not be fast, provided that the time of signal creation can be determined accurately (see Section 3.7.3). For example, the separation of ions in a mass spectrometer (time of flight) or electrons in an electron microscope may require microseconds or longer. Nevertheless, femtosecond time resolution has been achieved,186 187 because the ions or electrons are formed by a pulse of femtosecond duration (1 fs = 10 15 s). Several reports with recommended procedures for nanosecond flash photolysis,137,188-191 ultrafast electron diffraction and microscopy,192 crystallography193 and pump probe absorption spectroscopy194,195 are available and a general treatise on ultrafast intense laser chemistry is in preparation by IUPAC. 

Nanosecond Flash Photolysis Measurements.—A computer-controlled ns flash photolysis spectrometer has been described. " The system was employed in a study of the photochemistry of xanthene dyes in solution. A nitrogen laser was used to provide 2—3 mJ excitation pulses at 337.1 nm for a ns flash photolysis study of electron-transfer reactions of phenolate ions with aromatic carbonyl triplets. " A PDP II computer was used to control the transient digitizer employed for detection, and to subsequently process the data. A nanosecond transient absorption spectrophotometer has been constructed using a tunable dye laser in a pulse-probe conflguration with up to 100 ns probe delayA method for reconstructing the time-resolved transient absorption was discussed and results presented for anthracene in acetonitrile solution. The time-resolution of ns flash photolysis may be greatly increased by consideration of the integral under the transient absorption spectrum. Decay times comparable to or shorter than the excitation flash may be determined by this method. 

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