Application of the method of molecular beam photofragmentation translational spectroscopy to the investigation of primary photochemical processes of polyatomic molecules is described.
介绍了分子束光破碎平动光谱法在多原子分子初级光化学过程研究中的应用。
{"title":"Molecular Beam Studies of Primary Photochemical Processes","authors":"Yuan‐Pern Lee","doi":"10.1155/LC.2.219","DOIUrl":"https://doi.org/10.1155/LC.2.219","url":null,"abstract":"Application of the method of molecular beam photofragmentation translational spectroscopy \u0000to the investigation of primary photochemical processes of polyatomic \u0000molecules is described.","PeriodicalId":296295,"journal":{"name":"Laser Chemistry","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1982-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125460754","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this communication, we wish to report on the use of synchronously mode-locked picosecond lasers in a pump-probe configuration for TL spectroscopy. The peak power for these picosecond lasers is very high and, of course, the fundamental of the dye laser (red beam) can be efficiently (~10%) doubled in frequency (U.V. beam) by second harmonic generation in nonlinear crystals. We use this generated U.V. beam as a probe to monitor the very weak absorption of the red beam. An arrangement [4] of the beams involving different waist positions for the pump and probe is used. This arrangement results in an enhancement of sensitivity (at least a factor of three to seven). Also, a different dependence of the signal on the cell position compared to the single beam method is obtained. Finally, we have obtained the Δν = 5 CH-stretching overtone absorption spectrum of liquid toluene with this method (see Figure 1). Suggestions are made regarding new applications of this picosecond pulse thermal lensing technique.
{"title":"Thermal Lensing Spectroscopy With Picosecond Pulse Trains and a New Dual Beam Configuration","authors":"J. Perry, E. Ryabov, A. Zewail","doi":"10.1155/LC.1.9","DOIUrl":"https://doi.org/10.1155/LC.1.9","url":null,"abstract":"In this communication, we wish to report on the use of synchronously mode-locked picosecond lasers in a pump-probe configuration for TL spectroscopy. The peak power for these picosecond lasers is very high and, of course, the fundamental of the dye laser (red beam) can be efficiently (~10%) doubled in frequency (U.V. beam) by second harmonic generation in nonlinear crystals. We use this generated U.V. beam as a probe to monitor the very weak absorption of the red beam. An arrangement [4] of the beams involving different waist positions for the pump and probe is used. This arrangement results in an enhancement of sensitivity (at least a factor of three to seven). Also, a different dependence of the signal on the cell position compared to the single beam method is obtained. Finally, we have obtained the Δν = 5 CH-stretching overtone absorption spectrum of liquid toluene with this method (see Figure 1). Suggestions are made regarding new applications of this picosecond pulse thermal lensing technique.","PeriodicalId":296295,"journal":{"name":"Laser Chemistry","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1982-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128413445","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The technique of Multiphoton Induced Chemistry (MPIC) has been employed to initiate ion-molecule chemistry of organic molecules in solution. We report one of the first examples of the use of liquid phase multiphoton ionization (MPI) to prepare organic cations, which then react with the solvent in ionmolecule processes. The products obtained in this chemical sequence are significantly different from those observed in conventional or multiphoton-induced neutral chemistry in the same solvent. The particular example explored in this work is the reactivity of the nitrobenzene cation in methanol solvent. Products of the ion-molecule chemistry, detected by gas chromatography/mass spectrometry, are phenol and benzyl alcohol. These products depend upon the square of the laser intensity. It is shown by ionization current measurements in a conductance cell, that ionic species are produced as precursors to the observed products. The implications of this application of MPI are briefly discussed. A preliminary report on the unimolecular chemistry of the highly excited neutral molecule is also included. The product of this channel is nitrosobenzene. It is shown, in this case, that the reactive state is most likely a highly vibrationally excited ground state molecule, not the lowest triplet level invoked in conventional photochemistry.
{"title":"UV MULTIPHOTON INDUCED CHEMISTRY OF NITROBENZENE IN SOLUTION","authors":"J. BelBruno, G. Siuzdak, S. North","doi":"10.1155/1990/42676","DOIUrl":"https://doi.org/10.1155/1990/42676","url":null,"abstract":"The technique of Multiphoton Induced Chemistry (MPIC) has been employed to initiate ion-molecule \u0000chemistry of organic molecules in solution. We report one of the first examples of the use of liquid phase \u0000multiphoton ionization (MPI) to prepare organic cations, which then react with the solvent in ionmolecule \u0000processes. The products obtained in this chemical sequence are significantly different from those \u0000observed in conventional or multiphoton-induced neutral chemistry in the same solvent. The particular \u0000example explored in this work is the reactivity of the nitrobenzene cation in methanol solvent. Products of \u0000the ion-molecule chemistry, detected by gas chromatography/mass spectrometry, are phenol and benzyl \u0000alcohol. These products depend upon the square of the laser intensity. It is shown by ionization current \u0000measurements in a conductance cell, that ionic species are produced as precursors to the observed \u0000products. The implications of this application of MPI are briefly discussed. A preliminary report on the \u0000unimolecular chemistry of the highly excited neutral molecule is also included. The product of this channel \u0000is nitrosobenzene. It is shown, in this case, that the reactive state is most likely a highly vibrationally \u0000excited ground state molecule, not the lowest triplet level invoked in conventional photochemistry.","PeriodicalId":296295,"journal":{"name":"Laser Chemistry","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115320305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present a theoretical description of the dynamics of vibrational wave packets in the 1g state of Xe2. As an illustration, a simulation of a picosecond pump excitation-probe ionization laser experiment is carried out. The initial wavepacket is calculated using an explicit modelling of the short-pulse excitation process and propagated for up to 160 picoseconds. Evidence of fractional and full revivals of the wavepacket has been found and analyzed. The time delayed ionization signal is simulated using first order perturbation theory and shows clear oscillations corresponding to the temporal development of the wavepacket.
{"title":"A Theoretical Study of theDynamics of Vibrational WavePackets in the 1g State Of Xe2","authors":"J. Castillo, K. L. Reid","doi":"10.1155/1999/49417","DOIUrl":"https://doi.org/10.1155/1999/49417","url":null,"abstract":"We present a theoretical description of the dynamics of vibrational wave packets in the 1g state of Xe2. As an illustration, a simulation of a picosecond pump excitation-probe ionization laser experiment is carried out. The initial wavepacket is calculated using an explicit modelling of the short-pulse excitation process and propagated for up to 160 picoseconds. Evidence of fractional and full revivals of the wavepacket has been found and analyzed. The time delayed ionization signal is simulated using first order perturbation theory and shows clear oscillations corresponding to the temporal development of the wavepacket.","PeriodicalId":296295,"journal":{"name":"Laser Chemistry","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115763170","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. Blease, R. Donovan, P. Langridge-Smith, T. Ridley
Two-photon spectra of the S1(Ã)–S0(X˜) transition of jet-cooled ortho-, meta- and para-xylene have been recorded in the region 43,000–37,000 cm−1 using resonance enhanced multiphoton ionization excitation. A full vibronic analysis for all three isomers has been carried out enabling the identification of several excited state vibrational frequencies for the first time. In particular, for ortho and para substitutions, a new, strong two-photon vibronic coupling mode ν19b has been identified, and the significance of this result is discussed. Some anomalies in the assignment of previously published spectra of the xylenes, and related disubstituted benzenes, have been observed and reassignments are suggested. In addition we show that the comparison of one and two-photon spectra provides a method for determining the mechanism by which totally symmetric fundamentals gain their intensity in one-photon spectra, namely either from Herzberg–Teller intensity stealing or due to favourable Franck–Condon overlap.
{"title":"(2+2) Resonance enhanced multiphoton ionization spectra of jet-cooled ortho-, meta- and para-xylene","authors":"T. Blease, R. Donovan, P. Langridge-Smith, T. Ridley","doi":"10.1155/LC.9.241","DOIUrl":"https://doi.org/10.1155/LC.9.241","url":null,"abstract":"Two-photon spectra of the S1(Ã)–S0(X˜) transition of jet-cooled ortho-, meta- and para-xylene have been recorded in the region 43,000–37,000 cm−1 using resonance enhanced multiphoton ionization excitation. A full vibronic analysis for all three isomers has been carried out enabling the identification of several excited state vibrational frequencies for the first time. In particular, for ortho and para substitutions, a new, strong two-photon vibronic coupling mode ν19b has been identified, and the significance of this result is discussed. Some anomalies in the assignment of previously published spectra of the xylenes, and related disubstituted benzenes, have been observed and reassignments are suggested. In addition we show that the comparison of one and two-photon spectra provides a method for determining the mechanism by which totally symmetric fundamentals gain their intensity in one-photon spectra, namely either from Herzberg–Teller intensity stealing or due to favourable Franck–Condon overlap.","PeriodicalId":296295,"journal":{"name":"Laser Chemistry","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117158990","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We studied the IR luminescence spectra of vibrationally excited CF2Cl2 molecules resulting from excitation of the ν1 (1098 cm−1) and ν8 (922 cm−1) modes with a pulsed CO2 laser. The nonequilibrium spectra obtained under pumping conditions where their equilibrium counterparts coincide (the number of the photons absorbed per molecule being the same) were found to differ considerably. We suppose that this difference is due to different types of vibrational distribution formed as a result of the IR laser pumping. When pumping the ν1 mode, excitation of the R-branch occurs, resulting in the molecules “sticking” on the lower vibrational levels, whereas in the case of the ν8 mode, it is the P-branch that gets excited so that the molecules become easy to raise to high-lying vibrational levels.
{"title":"IR-Luminescence of CF2Cl2 Molecules in Multiple-Photon Excitation With Co2-Laser Radiation","authors":"A. V. Dem’yanenko, G. A. Polyakov, A. Puretzky","doi":"10.1155/LC.8.123","DOIUrl":"https://doi.org/10.1155/LC.8.123","url":null,"abstract":"We studied the IR luminescence spectra of vibrationally excited CF2Cl2 molecules \u0000resulting from excitation of the ν1 (1098 cm−1) and \u0000ν8 (922 cm−1) modes with a pulsed CO2 laser. \u0000The nonequilibrium spectra obtained under pumping conditions where their equilibrium counterparts \u0000coincide (the number of the photons absorbed per molecule being the same) were found to differ considerably. \u0000We suppose that this difference is due to different types of vibrational distribution formed as a result of the IR laser pumping. \u0000When pumping the ν1 mode, excitation of the R-branch occurs, resulting in the \u0000molecules “sticking” on the lower vibrational levels, whereas in the case of the ν8 mode, \u0000it is the P-branch that gets excited so that the molecules become easy to raise to high-lying vibrational levels.","PeriodicalId":296295,"journal":{"name":"Laser Chemistry","volume":"72 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117231513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
An investigation of molecular weight distributions (MWDs) resulting from initiation of free radical polymerization by an arbitrary sequence of short laser pulses has been undertaken. The analytical expressions have been derived to calculate MWDs for a polymerization scheme that contains reactions of chain initiation, propagation and termination by recombination or disproportionation. The MWDs produced by pulse-periodic irradiation have been calculated for a wide range of initiating pulses repetition rates (f = 0.05–100 Hz). The MWD dynamics in the act of polymerization and the influence of the duration of polymerization pseudostationary regime establishment upon the MWD have also been studied. The suitability of the derived expressions for describing the MWD generated by CW radiation before and after the establishment of polymerization quasi-stationary regime has been considered.
{"title":"Molecular Weight Distribution Generated on Initiation of Free RadicalPolymerization by Sequence of Laser Pulses","authors":"A. Evseev, A. N. Nikitin","doi":"10.1155/1995/48258","DOIUrl":"https://doi.org/10.1155/1995/48258","url":null,"abstract":"An investigation of molecular weight distributions (MWDs) resulting from initiation of free radical polymerization by an arbitrary sequence of short laser pulses has been undertaken. The analytical expressions have been derived to calculate MWDs for a polymerization scheme that contains reactions of chain initiation, propagation and termination by recombination or disproportionation. The MWDs produced by pulse-periodic irradiation have been calculated for a wide range of initiating pulses repetition rates (f = 0.05–100 Hz). The MWD dynamics in the act of polymerization and the influence of the duration of polymerization pseudostationary regime establishment upon the MWD have also been studied. The suitability of the derived expressions for describing the MWD generated by CW radiation before and after the establishment of polymerization quasi-stationary regime has been considered.","PeriodicalId":296295,"journal":{"name":"Laser Chemistry","volume":"14 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120860711","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. P. Simonov, G. Abakumov, V. T. Yaroslavtzev, V. A. Lunchev, E. A. Fedorov
Photodissociation of molecular radical cations of toluenes C7 H 8 +· (I), C6H5 CD 3 +· (II), C7 D 8 +· (III), cycloheptatriene C7 H 8 +· (IV), and benzene has been studied by the method of two-pulse two-colour laser photolysis of molecules in a mass spectrometer using wavelengths 1064, 532, and 355 nm. The I ions formed due to sequential two-photon ionization of toluene molecules by the 266 nm radiation isomerize supposingly into 5-methylene-cyclohexadiene (VI). Two- and three-photon stepwise dissociation of the I and II isomers (VI and VI-d3, respectively) induced by the 1064 nm radiation has a resonance at the third overtone level of CH aliphatic bond stretching vibrations. Internal energy randomization in the two-photon dissociation is much less for VI-d3 as compared to VI. The mechanisms of isoenergetic dissociation (two- and one-photon processes induced by the 1064 and 532 nm radiations, respectively) are different: the one-photon decay via an electronically excited state proceeds considerably faster than the two-photon decomposition does in the ground state. The photodissociation cross sections have been determined. It has been shown that the intensity of CH stretching vibration overtones can be essentially higher for radical cations than for the neutral molecules.
{"title":"Multiple Photon High VibrationalCH Overtone Resonant andOne-Photon Dissociation ofToluene Radical Cation","authors":"A. P. Simonov, G. Abakumov, V. T. Yaroslavtzev, V. A. Lunchev, E. A. Fedorov","doi":"10.1155/LC.5.275","DOIUrl":"https://doi.org/10.1155/LC.5.275","url":null,"abstract":"Photodissociation of molecular radical cations of toluenes C7 H 8 +· (I), C6H5 CD 3 +· (II), \u0000C7 D 8 +· (III), cycloheptatriene C7 H 8 +· (IV), and benzene has been studied by the method \u0000of two-pulse two-colour laser photolysis of molecules in a mass spectrometer using \u0000wavelengths 1064, 532, and 355 nm. The I ions formed due to sequential two-photon \u0000ionization of toluene molecules by the 266 nm radiation isomerize supposingly into \u00005-methylene-cyclohexadiene (VI). Two- and three-photon stepwise dissociation of the I \u0000and II isomers (VI and VI-d3, respectively) induced by the 1064 nm radiation has a \u0000resonance at the third overtone level of CH aliphatic bond stretching vibrations. Internal \u0000energy randomization in the two-photon dissociation is much less for VI-d3 as compared \u0000to VI. The mechanisms of isoenergetic dissociation (two- and one-photon processes \u0000induced by the 1064 and 532 nm radiations, respectively) are different: the one-photon \u0000decay via an electronically excited state proceeds considerably faster than the two-photon \u0000decomposition does in the ground state. The photodissociation cross sections \u0000have been determined. It has been shown that the intensity of CH stretching vibration \u0000overtones can be essentially higher for radical cations than for the neutral molecules.","PeriodicalId":296295,"journal":{"name":"Laser Chemistry","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127231499","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Emission spectra of MgI and MgII from a plasma induced by the interaction of a laser pulse with the surface of aqueous solutions of MgCl 2 , were recorded by a time resolved spectroscopy method to obtain information on the processes involved in the formation and the evolution of the two different species. A kinetic model based on ion-electron recombination produced during the relaxation of the plasma is constructed with the aim to explain the origin and the temporal shift of observed Mg + and Mg emissions. Comparison with the experimental results is presented and discussed.
{"title":"Kinetics of Laser Induced Plasma on an Aqueous Surface","authors":"J. Ahmed, Z. B. Lakhdar, G. Taieb","doi":"10.1080/02786270215154","DOIUrl":"https://doi.org/10.1080/02786270215154","url":null,"abstract":"Emission spectra of MgI and MgII from a plasma induced by the interaction of a laser pulse with the surface of aqueous solutions of MgCl 2 , were recorded by a time resolved spectroscopy method to obtain information on the processes involved in the formation and the evolution of the two different species. A kinetic model based on ion-electron recombination produced during the relaxation of the plasma is constructed with the aim to explain the origin and the temporal shift of observed Mg + and Mg emissions. Comparison with the experimental results is presented and discussed.","PeriodicalId":296295,"journal":{"name":"Laser Chemistry","volume":"83 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127469258","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Porte, D. S. Moreno, M. Striano, M. Munñoz, J. García-Ramos, S. S. Cortés, E. Koudoumas
Laser ablation of deposited silver colloids, active in SERS, is carried out at three different laser wavelengths (KrF, XeCl and Nd:YAG at λ = 248, 308 and 532 nm respectively). Emission form excited neutral Ag and Na atoms, present in the ablation plume, is detected with spectral and temporal resolution. The expansion velocity of Ag in the plume is estimated in ~1×104m s−1. Low-fluence laser ablation of the colloids yields ionized species that are analyzed by time-of-flight mass spectroscopy. Na
{"title":"Laser Ablation Studies of Deposited Silver Colloids Active in SERS","authors":"R. Porte, D. S. Moreno, M. Striano, M. Munñoz, J. García-Ramos, S. S. Cortés, E. Koudoumas","doi":"10.1080/02786270212132","DOIUrl":"https://doi.org/10.1080/02786270212132","url":null,"abstract":"Laser ablation of deposited silver colloids, active in SERS, is carried out at three different laser wavelengths (KrF, XeCl and Nd:YAG at λ = 248, 308 and 532 nm respectively). Emission form excited neutral Ag and Na atoms, present in the ablation plume, is detected with spectral and temporal resolution. The expansion velocity of Ag in the plume is estimated in ~1×104m s−1. Low-fluence laser ablation of the colloids yields ionized species that are analyzed by time-of-flight mass spectroscopy. Na","PeriodicalId":296295,"journal":{"name":"Laser Chemistry","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124862559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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