Showing papers on "Excimer published in 1977"
TL;DR: In this paper, an interactive kinetic model for bound-free excimer lasers is described, with particular emphasis on the electron beam pumped rare gas systems, and the interaction of the photon field with excited states is examined in detail.
Abstract: An interactive kinetic model for bound-free excimer lasers is described, with particular emphasis on the electron beam pumped rare gas systems. Important kinetic processes and the interaction of the photon field with excited states are examined in detail. Application of the model to the xenon and krypton oscillators yields results which are in good agreement with experimentally observed quantities. It is found that the collisional coupling of the excimer singlet and triplet manifolds in combination with the losses arising from photoionization play an important role in determining the performance. Numerical values of the parameters used in the computational model are given.
91 citations
TL;DR: In this paper, the influence of the molecular weight on the relative quantum yield of the pyrene groups has been analyzed according to the general kinetic treatment of diffusion controlled quenching processes.
84 citations
TL;DR: In this paper, the authors investigated intramolecular excimer formation for three polystyrene model molecules (2,4-diphenylpentane, 2,4,6-triphenylheptane and 2, 4,6,8-tetraphenylnonane).
33 citations
TL;DR: In this paper, the authors investigated the triplet-triplet absorption of α,α-dinaphthylalkanes in 1,3-diphenylpropane at several temperatures.
Abstract: The excimer phosphorescence, delayed fluorescence, and triplet–triplet absorption of α,α‐dinaphthylalkanes have been investigated in isooctane at several temperatures. The results are consistent with the formation of intramolecular triplet excimers whose conformation is significantly different from that favored by singlet excimers. 1,3‐diphenylpropane displays only monomerlike phosphorescence in fluid media over a wide temperature range, indicating that the binding energy of this triplet excimer is considerably smaller than that for the triplet excimers of dinaphthylalkanes.
31 citations
TL;DR: In this article, it was shown that the conformation of the triplet excimer is significantly different from a sandwich-pair geometry favored by the singlet excimer, leading to an increased T1 → So radiative transition probability.
30 citations
TL;DR: In this paper, the mechanism of excimer formation and deactivation for isotactic and atactic polystyrenes, and isotactic poly(p-methylsternes) was studied by comparison of the rate parameters which were calculated from the fluorescence quenching and the decay time measurements of the excimer emission band.
Abstract: The mechanism of excimer formation and deactivation for isotactic and atactic polystyrenes, and isotactic and atactic poly(p-methylstyrenes) was studied by comparison of the rate parameters which were calculated from the fluorescence quenching and the decay time measurements of excimer emission band. The activation energy of excimer formation was obtained from the effect of temperature change on fluorescence intensity. The rate parameters of excimer formation for isotactic polymers are in the order of 109 s−1 and larger than those for atactic polymers. The activation energy for isotactic polymers is smaller than that for atactic polymers. These results show that isotactic polymers can form the excimer more easily than atactic polymers. The facility of excimer formation for isotactic polymers is interpreted as lower energy barrier required to achieve the excited excimer state.
28 citations
TL;DR: In this article, a density-dependent nonexponential decay caused by bimolecular excimer quenching with a measured rate constant of k?2±1×10−10 cm3 sec−1 molecule−1.
Abstract: The continuous emission bands of molecular mercury at 0.335 and 0.485 μm are excited in a pure mercury vapor by direct optical pumping of the weakly bound ground state molecules with a 5 nsec pulse of intense 0.266 μm radiation in order to study the radiative and collisional properties of the excited molecules at densities between 1014 and 1015 cm−3. Fluorescence time history of both bands are empirically analyzed in terms of dynamics governing the excited molecules. The analysis includes a density‐dependent nonexponential decay caused by bimolecular excimer quenching with a measured rate constant of k?2±1×10−10 cm3 sec−1 molecule−1. Because of interest in the mercury system as a potential laser medium, estimates of gain coefficients are derived from fluorescent power measurements. However, transmission measurements of the excited medium at 0.325 and 0.4416 μm show significant net loss due to excited state absorption with an estimated absorption cross section on the order of 10−17 cm2 at 0.325 μm. Energy storage limitations implied by the bimolecular excimer quenching are also examined.
27 citations
TL;DR: In this article, the surface of the lowest excited singlet state in methane was analyzed using a basis set composed of 4-31G augmented by a set of one s and three p Rydbergs.
26 citations
25 citations
TL;DR: In this article, the interaction between 3-methylindole (3-MeI) in cyclohexane with the polar molecules ethyl acetate (EA) and dimethylacetamide (DMA) was studied.
Abstract: The interaction between 3-methylindole (3-MeI) in cyclohexane with the polar molecules ethyl acetate (EA) and dimethylacetamide (DMA) was studied. The kinetic analysis of the fluorescence data shows that 3-MeI forms an excited state complex with EA in a diffusion controlled process. The temperature dependence of the exciplex formation indicates that its dissociation rate constant too is of appreciable magnitude. UV, IR and fluorescence measurements all indicate that DMA forms complexes with 3-MeI both in the ground and in the excited states. The latter complex is rather strong i.e. its dissociation rate is negligibly small. The findings imply that the fluorescence properties of tryptophan residues within a protein often must be determined by their interaction with neighboring polar groups rather than by the degree to which they are exposed to the ambient solution.
25 citations
TL;DR: In this article, a pulse radiolysis study of polyethylene has been carried out with the main aim of investigating energy transfer from the irradiated polymer to aromatic solutes present at low concentration.
TL;DR: In this article, the influence of concentration on the fluorescence of perylene dissolved in a rigid polymer matrix has been investigated, and the observations are interpreted in terms of excitation transfer by a Forster inductive resonance mechanism, followed by trapping at a site which has a neighbour near enough to form an excited complex.
Abstract: The influence of concentration on the fluorescence of perylene dissolved in a rigid polymer matrix has been investigated. As the concentration increases, the monomer fluorescence is quenched and a new emission at lower energies is observed. Diffusional quenching of the type often encountered in fluid solutions cannot occur in this case and the observations are interpreted in terms of excitation transfer by a Forster inductive resonance mechanism, followed by trapping at a site which has a neighbour near enough to form an excited complex.
09 Nov 1977
TL;DR: In this article, a study of the spectroscopy and photochemistry of crystalline 9-cyanoanthracene is reported, and the experimental observations are in good agreement with the predictions of theories based on the strong exciton-phonon coupling.
Abstract: A study of the spectroscopy and photochemistry of crystalline 9-cyanoanthracene is reported. This crystal gives rise to excimer emission; at 77 K the excimer has a lifetime of 160 ±5 ns and the emission spectrum is of gaussian shape. There is, prior to reaction, transfer of excitation energy by a process occurring at the excimer—exciton level and involving an activation energy of about 420 cm−1 . Radiationless deactivation of the excimer involves an activation energy of 660 cm −1 . These experimental observations are in good agreement with the predictions of theories based on the model of strong exciton—phonon coupling. The photoreaction occurs at specific sites which are believed to be head-to-tail defects.
TL;DR: In this article, a model for the kinetics of NF3 and N2F2 in an excimer laser is presented, followed by a mass spectrometer for the appearance of NF2 and NF3.
Abstract: Disappearance of NF3 and appearance of NF2 and N2F2 in an excimer laser is followed quantitatively with a mass spectrometer. A model for the kinetics is presented.
TL;DR: In this article, a method was developed for the determination of the extent of alternation in copolymers in which one of the comonomers contains a fluorescent chromophore capable of intramolecular excimer formation.
Abstract: A novel method has been developed for the determination of the extent of alternation in copolymers in which one of the comonomers contains a fluorescent chromophore capable of intramolecular excimer formation. The ratio of excimer to monomer fluorescence intensity is linearly correlated with the fraction of adjacent fluorescent chromphores to isolated fluophores on the chain. The method is illustrated for the case of styrene-acrylonitrile copolymers.
TL;DR: It was shown that energy migration via excimer does not take place and energy of the excimer is localized, which means that singlet energy migrates among more naphthyl groups with increasing naphTHyl groups in the polymer chain.
Abstract: Energy transfer in the singlet state was studied in solution at 25 degrees C for poly(beta-1-naphthylmethyl L-aspartate) and copolymers of beta-1-naphthylmethyl L-aspartate and gamma-benzyl L-glutamate. Transfer efficiencies, migration coefficients, migration lengths, and interaction radii were determined from the quenching studies using biacetyl as a quencher. The migration coefficient increases with increasing naphthyl groups in the copolymers. This means that singlet energy migrates among more naphthyl groups with increasing naphthyl groups in the polymer chain. Interaction radius for the fluorescence quenching by biacetyl was estimated to be in the range of 5.8 to 8.9 A irrespective of whether energy donor is monomer or excimer. Moreover, it was shown that energy migration via excimer does not take place and energy of the excimer is localized.
TL;DR: The emission properties of poly(9-vinylphenanthrene) (PVPh), poly( 9-phenanthryl methacrylate) (pPhMA), and poly[2]-ethyl vinyl ether] were investigated in solution as discussed by the authors.
Abstract: The emission properties of 9-ethylphenanthrene (EPh), poly(9-vinylphenanthrene) (PVPh), poly(9-phenanthryl methacrylate) (PPhMA), and poly[2-(9-phenanthryl)ethyl vinyl ether] were investigated in solution. These vinyl polymers showed no clear excimer fluorescence in the longer-wavelength region. Both the fluorescence quantum yield and the lifetime of PVPh decreased largely with an increase in temperature at higher temperatures. This suggests that PVPh forms an excimer which has a low fluorescence quantum yield. The fluorescence properties of PPhMA and PPhEVE, in which Ph chromophores are widely spaced on the skeletal chains, indicated little interaction between neighboring Ph chromophores in the singlet state. This results from the nature of Ph, in whith it is difficult to form an excimer. The phosphorescence spectrum and its lifetime of PPhEVE indicated a presence of a weak interaction between neighboring Ph chromophores in the triplet state. PVPh and PPhEVE showed a delayed fluorescence resulting from a...
TL;DR: In this paper, the temperature dependence of the ratio, α, of the rates of formation of excimer (1D*) and excited monomer (1M*) following triplet-triplet annihilation of aromatic molecules, is examined using two models.
Abstract: The temperature dependence of the ratio, α, of the rates of formation of excimer (1D*) and excited monomer (1M*) following triplet–triplet annihilation of aromatic molecules, is examined using two models. The first assumes that the annihilation occurs solely in a solvent cage and leads to 1D* and (1M* and 1M) formation; it includes separation and re-encounter of 1M* and 1M. This model produces only a weak dependence of α on temperature. The second model permits, in addition, long range annihilation to form 1M* and 1M with a rate constant which falls off exponentially with separation. It uses the diffusion model developed recently by Pilling and Rice and incorporates an analysis of encounter/re-encounter processes for 1M* and 1M formed by both the long range and cage processes. This model is able to reproduce the experimental temperature dependence with realistic parameters for the long range interaction.
TL;DR: In this paper, a conventional and new approximation which does not depend on the experimental set-up response functions has been used for evaluating pyrene excimer association energy W DM and other pyrene parameters.
TL;DR: In this article, the rate of excited state complex formation of indoles with dimethylformamide is shown to be a function of the group appended to the indole ring at the 3- or 5-position.
Abstract: . The quenching of the excited state of indoles by small polar molecules is believed to occur via the formation of excited state complexes. The rate of excited state complex formation of indoles with dimethylformamide is shown to be a function of the group appended to the indole ring at the 3- or 5-position. Substituents which can strengthen the charge transfer character of the exciplex are observed to enhance the rate of fluorescence quenching. In contrast to other amides, dimethylformamide appears to be a moderately good quencher of indole fluorescence, and may be a useful probe for proteins.
TL;DR: In this article, the use of lasing in atomic and molecular lines, that occurs in one burst, was investigated in investigations of the excitation kinetics of excimer states under the conditions of a high-pressure electric discharge.
Abstract: Lasing in atomic lines of noble gases and fluorine, prior to excimer radiation, was observed in an electric discharge ArF/XeF excimer laser. Some Ar/Xe lines end at metastable levels, which are very important for the formation of ArF/XeF excimer molecules. Five new lasing lines of atomic fluorine have been obtained. Consideration is given to the use of lasing in atomic and molecular lines, that occurs in one burst, in investigations of the excitation kinetics of excimer states under the conditions of a high-pressure electric discharge.
TL;DR: In this paper, 2-Phenyl-5-(p-vinyl)phenyloxazole (POS) has been synthesized and copolymers of POS with styrene and the homopolymer poly-POS have been prepared.
Abstract: 2-Phenyl-5-(p-vinyl)phenyloxazole (POS) has been synthesized. Copolymers of POS with styrene and the homopolymer poly–POS have been prepared. The polymers have been characterized through measurements of fluorescence decay times (using synchrotron radiation for excitation) and examination of excimer formation in the homopolymer. Fluorescence decay times of 0.6(±0.4) nsec and 9 (±0.2) nsec have been recorded at 298°K in toluene solution for monomer and excimer, respectively. Poly-POS exhibits excimer formation characterized by an activation energy of 5.9(±0.5) kJ/mole and a binding energy of 17.0(±1.0) kJ/mole.
TL;DR: In this article, the potential energy curves of the electronic interactions between excimer and electron acceptor molecule, and between exciplex and electron donor molecule were constructed for the 1,4-dicyanobenzene (DCB) and naphthalene system.
Abstract: Semiempirical SCF-MO-CI caluculation was carried out for the 1,4-dicyanobenzene (DCB) and naphthalene system which is known to form exciplex (DA)* and triple exciplex (D2A)*. Potential energy curves of the electronic interactions between excimer and electron acceptor molecule, and between exciplex and electron donor molecule were constructed. The results show that the array of component molecules in the triple exciplex is DDA, and the stabilization energy of triple exciplex is ≈0.4 eV from the excimer and ≈0.2 eV from the exciplex. They are in line with results reported on the experiment of exciplex and triple exciplex formation.
TL;DR: In this paper, a gas-discharge XeF, XeCl, and KrF laser, emitting ultraviolet radiation, was constructed and the emission spectra of the laser were determined.
Abstract: Gas-discharge XeF, XeCl, and KrF lasers, emitting ultraviolet radiation, were constructed. Stimulated emission from a discharge in XeCl (lambda/sub 1/=3081.6 A, lambda/sub 2/=3079.2 A) was observed for the first time. The emission spectra of the lasers were determined and a structure was found in the XeF laser spectrum (six lines in the 3487.5--3585.4 A range). The energy per pulse was 2, 1, and 0.5 mJ and the duration of the laser pulses was 15, 10, and 17 nsec for XeF, XeCl, and KrF lasers, respectively.
Patent•
14 Nov 1977TL;DR: In this article, a gaseous sample containing molecules of the gas to be detected is simultaneously subjected to two photon beams which, for example, may be generated by lasers, and the wave length of the first photon beam corresponds to the energy separation between the ground electronic state and an excited electronic state of the molecular gas.
Abstract: An arrangement for detecting low concentrations of molecular gases. A gaseous sample containing molecules of the gas to be detected is simultaneously subjected to two photon beams which, for example, may be generated by lasers. The wave length of the first photon beam corresponds to the energy separation between the ground electronic state and an excited electronic state of the molecular gas and the second photon beam contains energy in a wave length corresponding to the energy separation between the excited electronic state and the ionization limit of the molecule. Detection of the amount of ionization achieved is a measure of the concentration of the molecular gas in the sample. Simultaneous identification of the particular wave lengths causing the transition of the molecules from the ground energy state to the excited state provides an additional parameter identifying the molecules.
TL;DR: In this article, the shape and position of fluorescence bands observed in pyrene crystals and pyrenophanes are interpreted in terms of the structural differences in the geometry of the excimer state.
TL;DR: In this article, the authors used time resolved fluorescence spectroscopy to study the evolution of the excimer system following a 4 ns optical excitation pulse and observed significant differences between the mercury excimer fluorescence produced by electron beam and optical fluorescence.
TL;DR: In this paper, the specific sensitization of excimer fluorescence of pyrene, 2:3 dimethylnaphthalene and fluorene in polystyrene fluffs by a concerted mechanism involving electronic energy transfer from singlet molecular oxygen was reported.