Kinetics Of Photodissociation Research Articles

Influence of Illumination Spectrum on Dissociation Kinetics of Iron–Boron Pairs in Silicon

Photodissociation kinetics of iron–boron (FeB) pairs in boron‐doped Czochralski silicon is studied experimentally using different light sources. It is shown that the FeB dissociation rate depends not only on integrated light intensity and overall carrier generation rate, but also on spectral composition of illumination. The value of the material constant of dissociation K varies and has been determined to be within s. The investigation reveals an increase in the dissociation rate with increase in photon energy. The results indicate that recombination‐enhanced defect reaction is the primary factor in the second stage of pair dissociation.

A 700nm LED Light Activated Ru(II) Complex Destroys Tumor Cytoskeleton via Photosensitization and Photocatalysis.

Photoactivable chemotherapy (PACT) using metallic complexes provides spatiotemporal selectivity over drug activation for targeted anticancer therapy. However, the poor absorption in near-infrared (NIR) light region of most metallic complexes renders tissue penetration challenging. Herein, an NIR light triggered dinuclear photoactivable Ru(II) complex (Ru2) is presented and the antitumor mechanism is comprehensively investigated. The introduction of a donor-acceptor-donor (D-A-D) linker greatly enhances the intramolecular charge transition, resulting in a high molar extinction coefficient in the NIR region with an extended triplet excited state lifetime. Most importantly, when activated by 700nm NIR light, Ru2 exhibits unique slow photodissociation kinetics that facilitates synergistic photosensitization and photocatalytic activity to destroy diverse intracellular biomolecules. In vitro and in vivo experiments show that when activated by 700nm NIR light, Ru2 exhibits nanomolar photocytotoxicity toward 4T1 cancer cells via the induction of calcium overload and endoplasmic reticulum (ER) stress. These findings provide a robust foundation for the development of NIR-activated Ru(II) PACT complexes for phototherapeutic application.

Photodissociation and kinetics of bis-2-benzylidenemalononitrile (BBM) in different micelles environment

In present work, photodissociation kinetics of selective CC bond in BBM is investigated in different micelles concentration. In polar solvents, rate of photodissociation (k) is relatively lower compared to H2O solvent under similar condition. The rate of photodissociation (k) is enhanced with increase of aqueous CTAB concentration and found to be highly sensitive to aqueous CTAB concentration. It is clear that micelle concentration and hydrophobic region plays significant role on enhancing rate of photodissociation. Crucial role of hydrophobic region in micelle has been discussed and confirmed by experimental results.

A tryptophan synchronous and normal fluorescence study on bacteria inactivation mechanism

The UV photodissociation kinetics of tryptophan amino acid, Trp, attached to the membrane of bacteria, Escherichia coli and Bacillus subtilis, have been studied by means of normal and synchronous fluorescence. Our experimental data suggest that the fluorescence intensity of Trp increases during the first minute of irradiation with 250 nm to ∼ 280 nm, 7 mW/cm2 UV light, and subsequently decreases with continuous irradiation. During this short, less than a minute, period of time, 70% of the 107 cell per milliliter bacteria are inactivated. This increase in fluorescence intensity is not observed when tryptophan is in the free state, namely, not attached to a protein, but dissolved in water or saline solution. This increase in fluorescence is attributed to the additional fluorescence of tryptophan molecules formed by protein unfolding, the breakage of the bond that attaches Trp to the bacterial protein membrane, or possibly caused by the irradiation of 2 types of tryptophan residues that photolyze with different quantum yields.

Photodissociation kinetics of the isobutanal radical cation: a combined experimental and theoretical study

Main photodissociation pathways of isobutanal radical cation generated by (2 + 1) REMPI process.

Coordination Numbers of Hydrated Divalent Transition Metal Ions Investigated with IRPD Spectroscopy

Hydration of the divalent transition metal ions, Mn, Fe, Co, Ni, Cu, and Zn, with 5-8 water molecules attached was investigated using infrared photodissociation spectroscopy and photodissociation kinetics. At 215 K, spectral intensities in both the bonded-OH and free-OH stretch regions indicate that the average coordination number (CN) of Mn(2+), Fe(2+), Co(2+), and Ni(2+) is ~6, and these CN values are greater than those of Cu(2+) and Zn(2+). Ni has the highest CN, with no evidence for any population of structures with a water molecule in a second solvation shell for the hexa-hydrate at temperatures up to 331 K. Mn(2+), Fe(2+), and Co(2+) have similar CN at low temperature, but spectra of Mn(2+)(H(2)O)(6) indicate a second population of structures with a water molecule in a second solvent shell, i.e., a CN < 6, that increases in abundance at higher temperature (305 K). The propensity for these ions to undergo charge separation reactions at small cluster size roughly correlates with the ordering of the hydrolysis constants of these ions in aqueous solution and is consistent with the ordering of average CN values established from the infrared spectra of these ions.

Zn2+ Has a Primary Hydration Sphere of Five: IR Action Spectroscopy and Theoretical Studies of Hydrated Zn2+ Complexes in the Gas Phase

Complexes of Zn(2+)(H(2)O)(n), where n = 6-12, are examined using infrared photodissociation (IRPD) spectroscopy, blackbody infrared radiative dissociation (BIRD), and theory. Geometry optimizations and frequency calculations are performed at the B3LYP/6-311+G(d,p) level along with single point energy calculations for relative energetics at the B3LYP, B3P86, and MP2(full) levels with a 6-311+G(2d,2p) basis set. The IRPD spectrum of Zn(2+)(H(2)O)(8) is most consistent with the calculated spectrum of the five-coordinate MP2(full) ground-state (GS) species. Results from larger complexes also point toward a coordination number of five, although contributions from six-coordinate species cannot be ruled out. For n = 6 and 7, comparisons of the individual IRPD spectra with calculated spectra are less conclusive. However, in combination with the BIRD and laser photodissociation kinetics as well as a comparison to hydrated Cu(2+) and Ca(2+), the presence of five-coordinate species with some contribution from six-coordinate species seems likely. Additionally, the BIRD rate constants show that Zn(2+)(H(2)O)(6) and Zn(2+)(H(2)O)(7) complexes are less stable than Zn(2+)(H(2)O)(8). This trend is consistent with previous work that demonstrates the enthalpic favorability of the charge separation process forming singly charged hydrated metal hydroxide and protonated water complexes versus loss of a water molecule for complexes of n ≤ 7. Overall, these results are most consistent with the lowest-energy structures calculated at the MP2(full) level of theory and disagree with those calculated at B3LYP and B3P86 levels.

Fluorescence and Photodissociation of Rhodamine 575 Cations in a Quadrupole Ion Trap

The fluorescence and photodissociation of rhodamine 575 cations confined to a quadrupole ion trap are observed during laser irradiation at 488 nm. The kinetics of photodissociation is measured by time-dependent mass spectra and time-dependent fluorescence. The rhodamine ion signal and fluorescence decay are studied as functions of buffer gas pressure, laser fluence, and irradiation time. The decay rates of the ions in the mass spectra agree with decay rates of the fluorescence. Some of the fragment ions also fluoresce and further dissociate. The photodissociation rate is found to depend on the incident laser fluence and buffer gas pressure. The implications of rapid absorption/fluorescence cycling for photodissociation of dye-labeled biomolecular ions under continuous irradiation are discussed.

Photodissociation of bromochlorobenzenes

The photodissociation kinetics of 2-, 3- and 4-bromochlorobenzene (BrClPh) and bromo-3,5-dichlorobenzene (Br-diClPh) have been studied in a molecular beam following excitation at 270 nm using femtosecond pump-probe spectroscopy. The kinetics and the dissociation dynamics in the BrClPhs were found to resemble the BrFPhs much more than the BrBrPhs. In 2- and 3-BrClPh two dissociation channels were observed, whereas 4-BrClPh and Br-3,5-diClPh dissociates via only one channel. The time constant for channel one, present in all molecules, depends on the number of chlorine atoms and their position. The absence of a second channel in 4-BrClPh is a general property among mixed Br-(Br, Cl or F)-Phs and is likely to be due to a dissociation channel involving a triplet excitation.

Discovery of benzene cation in a very long-lived excited electronic state

Presence of benzene cation in a long-lived excited electronic state at ∼2.3 eV above the ground state was found through photodissociation kinetics and charge exchange ionization mass spectrometry. The lifetime of this state seems to be longer than 10 μs, maybe much longer. The experimental energy level of this state suggests that B̃ 2E2g is the best candidate. The radiative transition from the latter state to the ground state, B̃ 2E2g→X̃ 2E1g, is electric dipole forbidden. Then, a very long lifetime requires an inefficient radiationless decay of the state. This is in contrast with the very fast decay proposed previously to account for the lack of fluorescence from the B̃ 2E2g state. The present finding opens the possibility of studying a new excited state chemistry.

Energetics from Slow Infrared Multiphoton Dissociation of Biomolecules

Photodissociation kinetics of the protonated pentapeptide leucine enkephalin measured using a cw CO(2) laser and a Fourier-transform mass spectrometer are reported. A short induction period, corresponding to the time required to raise the internal energy of the ion population to a (dissociating) steady state, is observed. After this induction period, the dissociation data are accurately fit by first-order kinetics. A plot of the log of the unimolecular dissociation rate constant, k(uni), as a function of the log of laser power is linear at low laser powers (<9 W, k(uni) <0.05 s(-1)), but tapers off at high laser power (9-33 W, k(uni) = 0.05-7 s(-1)). The entire measured dissociation curve can be accurately fit by an exponential function plus a constant. The experiment is simulated using a master equation formalism. In the model, the laser radiation is described as an energetically flat-topped distribution which is spatially uniform. This description is consistent with experimental results which indicate that ion motion within the cell averages out spatial inhomogeneities in the laser light. The model has several adjustable parameters. The effect of varying these parameters on the calculated kinetics and power dependence curves is discussed. A procedure for determining a limited range of threshold dissociation energy, E(o), which fits both the measured induction period and power dependence curves, is presented. Using this procedure, E(o) of leucine enkephalin is determined to be 1.12-1.46 eV. This result is consistent with, although less precise than, values measured previously using blackbody infrared radiative dissociation. Although the blackbody dissociation results were used as a starting point to search for fits of the master equation model to experiment, these results demonstrate that it is, in principle, possible to determine a limited range of E(o) from slow infrared multiphoton dissociation data alone.

Internal energy content of n-butylbenzene, bromobenzene, iodobenzene and aniline molecular ions generated by two-photon ionization at 266 nm. A photodissociation study

A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd.

Internal energy content of n‐butylbenzene, bromobenzene, iodobenzene and aniline molecular ions generated by two‐photon ionization at 266 nm. A photodissociation study

A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright © 1999 John Wiley & Sons, Ltd.

Laser Ionization Measurements of the Photodissociation Kinetics of Jet-Cooled Benzaldehyde

The kinetics of benzaldehyde dissociation into benzene and carbon monoxide following excitation to the S2 state has been investigated under jet-cooled conditions by two-color laser ionization mass spectrometry using a pump−probe technique. A kinetic model has been proposed to explain the observed biexponential decay of the benzaldehyde signal and the single-exponential growth of the benzene product signal in terms of a sequential decay of two excited states of benzaldehyde, one of which leads to formation of benzene molecules in its lowest triplet state. Reactant disappearance and product appearance rates were determined for a number of vibronic transitions in the first 2000 cm-1 energy region of the S2 state. At the S2 origin the decay rate of the short-lived state of benzaldehyde was found to be 1.2 × 106 s-1.

Reinvestigation of the photodissociation kinetics of m-iodotoluene molecular ion

Photodissociation kinetics of the m-iodotoluene molecular ion has been investigated on a nanosecond time scale by mass-analyzed ion kinetic energy spectrometry. Photodissociation rate constants have been determined at molecular ion internal energies of 3.7–4.3 eV. The influence of the collisional relaxation of the molecular ion occurring in the ion source on the rate constant has been corrected, which was not considered in the previous photodissociation experiment. The kinetic energy release distributions (KERDs) determined from the ion kinetic energy profiles are composite due to the participation of two competing reaction channels, one leading to the formation of m-tolyl ion and the other to tropylium ion. By separating these bimodal KERDs, the branching ratios for the two channels have been obtained. From the overall rate constants and the branching ratios, rate constants for each channel have been determined on a nanosecond time scale. It has been found that the rate-energy data for each channel can be explained adequately by the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The production of m-tolyl ion proceeds via a loose transition state while that of tropylium ion proceeds via a tight transition state. Refined experimental data together with the microsecond data reported by Lin and Dunbar have been found to be essential to arrive at the correct mechanistic pictures for these reactions

Photodissociation of Chlorobenzene Molecular Ion: Investigation of Entropy Bottleneck in Ionic Systems. 2

Photodissociation kinetics of iodobenzene molecular ion has been investigated by mass-analyzed ion kinetic energy spectrometry (MIKES). A method has been devised to correct for the influence of collisional relaxation of the molecular ion occurring in the ion source on the rate constant. Theoretical analysis of the present rate-energy data on a nanosecond time scale together with previous microsecond data has found no firm evidence to support the transition state switching from an orbiting transition state to a tight transition state, especially at internal energy well above the threshold. At internal energy near the threshold, the transition-state switching has been found possible when the best literature value of 2.38 eV was used as the energy barrier

Photodissociation of iodobenzene molecular ion: investigation of entropy bottleneck of ionic systems

Photodissociation kinetics of iodobenzene molecular ion has been investigated by mass-analyzed ion kinetic energy spectrometry (MIKES). A method has been devised to correct for the influence of collisional relaxation of the molecular ion occurring in the ion source on the rate constant. Theoretical analysis of the present rate-energy data on a nanosecond time scale together with previous microsecond data has found no firm evidence to support the transition state switching from an orbiting transition state to a tight transition state, especially at internal energy well above the threshold. At internal energy near the threshold, the transition-state switching has been found possible when the best literature value of 2.38 eV was used as the energy barrier

Heterogeneous distributions and dispersive photodissociation rates of benzo[a]pyrene diol-epoxide enantiomer-DNA and -poly (dG-dC) · poly (dG-dC) adducts

Two types of heterogeneity of adducts are illustrated and discussed utilizing non-line narrowed ( S 2← S 0 laser excitation) and line-narrowed (excitation into the (0,0) origin band) fluorescence spectra at low temperatures. The first type (type A) is due to structurally distinct and/or energetically inequivalent conformers. The second one (type B) is provided by an inhomogeneous environment of DNA and polynucleotides. In light of the above, the non-exponential photodissociation kinetics of the (±)- anti-BPDE-DNA and -polynucleotide adducts have been reanalyzed in terms of a dispersive first order chemical reaction, where the inhomogeneous effects are explicitly included. It is demonstrated that the DNA structure shows considerable inhomogeneous broadening, and that type B heterogeneity is responsible for the dispersive photodissociation process. The latter is accounted for by a Gaussian distribution of activation energies, with the center of the distribution at ≈ 600 meV and the full width at half-maximum equal to ≈ 50 meV (≈ 2 kT). Photolabile (±)- anti-BPDE- DNA and -polynucleotide adducts are identified as quasi-intercalated (site 1) (+)- and (−)- cis-BPDE. The calculated concentrations of cis-BPDE adducts in DNA and polynucleotides from the kinetic data are in very good agreement with the cis-BPDE adduct concentrations obtained from the spectral and/or chemical analysis. The average photodissociation rate and the photodissociation quantum yield of cis- and trans-BPDE adducts are also estimated.

Photodissociation and structures of [C6H4]+ ˙ ions generated from cyanobenzene and other precursors

AbstractPrevious work on the electron impact induced loss of hydrogen cyanide from the radical cations of cyanobenzene has revealed that ring opening is important in the formation of the corresponding [C6H4]+ ˙ ions. Photodissociation experiments now show that these [C6H4]+ ˙ ions and those generated from 2‐ethynylpyridine, 1,3‐hexadiyn‐6‐nitrile and 1,2‐diiodobenzene all photodissociate in the visible region to [C4H2]+ ˙. The corresponding photodissociation spectra are all the same and have a maximum at about 370 nm, in agreement with spectra of ions with three conjugated double or triple bonds. Owing to the high reactivity, the low photodissociation rate and, possibly, the internal energy of the ions, the photodissociation kinetics are too complicated to be solved. The experiments nevertheless show that at least a major fraction of the [C6H4]+ ˙ ions has a ring‐opened structure. This conclusion is supported by MNDO calculations, which indicate that the heats of formation of the possible acyclic structures are about 150 kJ mol−1 lower than those of the o‐, m‐ and p‐benzyne structures.

ChemInform Abstract: The Kinetics of Photodissociation of Tungsten Hexacarbonyl.

ChemInformVolume 18, Issue 24 Preparative Organic Chemistry ChemInform Abstract: The Kinetics of Photodissociation of Tungsten Hexacarbonyl. C. H. LANGFORD, C. H. LANGFORD Can. Cent. Picosecond Flash Photolysis, Concordia Univ., Montreal, Que., H3G 1M8, Can.Search for more papers by this authorC. MORALEJO, C. MORALEJO Can. Cent. Picosecond Flash Photolysis, Concordia Univ., Montreal, Que., H3G 1M8, Can.Search for more papers by this authorD. K. SHARMA, D. K. SHARMA Can. Cent. Picosecond Flash Photolysis, Concordia Univ., Montreal, Que., H3G 1M8, Can.Search for more papers by this author C. H. LANGFORD, C. H. LANGFORD Can. Cent. Picosecond Flash Photolysis, Concordia Univ., Montreal, Que., H3G 1M8, Can.Search for more papers by this authorC. MORALEJO, C. MORALEJO Can. Cent. Picosecond Flash Photolysis, Concordia Univ., Montreal, Que., H3G 1M8, Can.Search for more papers by this authorD. K. SHARMA, D. K. SHARMA Can. Cent. Picosecond Flash Photolysis, Concordia Univ., Montreal, Que., H3G 1M8, Can.Search for more papers by this author First published: June 16, 1987 https://doi.org/10.1002/chin.198724101Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume18, Issue24June 16, 1987 RelatedInformation