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Cr CO 6 was investigated by X ray absorption spectroscopy. The spectral signature at the metal edge provides information about the back bonding of the metal in this class of complexes. Among the processes it participates in is ligand substitution in which a carbonyl ligand is ejected through excitation to a metal to ligand charge transfer MLCT band. The unsaturated carbonyl Cr CO 5 is stabilized by solution media in square pyramidal geometry and further reacts with the solvent. Multi site specific probing after photoexcitation was used to investigate the ligand substitution photoreaction process which is a common first step in catalytic processes involving metal carbonyls. The data were analysed with the aid of TD DFT computations for different models of photoproducts and signatures for ligand rearrangement after substitution were found. The rearrangement was found to occur in about 790 ps in agreement with former studies of the photoreaction

A slow and clean fluorine atom beam source is one of the essential components for the low-collision energy scattering experiment involving fluorine atom. In this work, we describe a simple but effective photolysis fluorine atom beam source based on ultraviolet laser photolysis, the performance of which was demonstrated by high-resolution time-of-flight spectra from the reactive scattering of F+HD. This beam source paved the way for studies of low energy collisions with fluorine atoms.

Photolysis of NO2 is the only major pathway for O3 formation as products from the reaction of OH and NO under atmospheric conditions in competition to the formation of HONO has been investigated experimentally and theoretically. Experiments have been carried out by directly measuring the formation of HO2 radicals using laser photolysis coupled to cw-CRDS. OH radicals have been generated from the reaction of F atoms with H2O, and absolute HO2 and OH profiles have been recorded at different NO concentrations. The potential energy surface has been calculated and the rate constant has been obtained from RRKM master equation modeling. Both experiment and theory show that the OH + NO reaction in the presence of O2 bath gas is not a competitive source of HO2 + NO2.

IR diode laser spectroscopy was used to detect the products of HCNO (fulminic acid) photolysis at 193 nm. Six product channels are energetically possible at this photolysis wavelength: O + HCN, H + NCO/CNO, CN + OH, CO + NH, NO + CH and HNCO. In some experiments, isotopically labeled 15 N 18 O, C 2 D 6 or C 6 H 12 reagents were included into the photolysis mixture in order to suppress and/or redirect possible secondary reactions. HCN, OC 18 O, 15 N 15 NO, CO, DCN and HNCO molecules were detected upon laser photolysis of HCNO/reagents/buffer gas mixtures. Analysis of the yields of product molecules leads to the following photolysis quantum yields: ϕ 1a (O + HCN) = 0.38 ± 0.04, ϕ 1b (H + (NCO)) = 0.07 ± 0.02, ϕ 1c (CN + OH) = 0.24 ± 0.03, ϕ 1d (CO + NH(a 1 Δ)) ϕ 1e (HNCO) = 0.02 ± 0.01 and ϕ 1f (CH + NO) = 0.21 ± 0.1, respectively.

The rate constant of the reaction C 2 H 5 O 2 + OH → Products has been measured at T = 296 K using laser photolysis coupled to CRDS and LIF. C 2 H 5 O 2 was generated from the reaction of Cl-atoms with C 2 H 6 at 55 Torr O 2 , whereby Cl-atoms were generated by 248 nm photolysis of (COCl) 2 . OH radicals were generated simultaneously by photolysing H 2 O 2 . The initial Cl-concentration (and hence C 2 H 5 O 2 ) was determined in separate experiments by replacing C 2 H 6 by CH 3 OH and thus conversion of Cl-atoms to HO 2 . The time-resolved OH decay was detected in excess of C 2 H 5 O 2 . A fast rate constant of k = (1.2 ± 0.3) × 10 −10 cm 3 s −1 was determined.

The photochemical reactions of o-ethoxybenzophenone (R-1) and o-2,2,2-trifluoroethoxybenzophenone (R-2) in cyclohexane solutions of 0.7 M pyridine have been investigated using time-resolved laser flash photolysis to understand diastereoselectivity in the photocyclization of the two compounds. Whereas the formation times of biradical intermediates (7 ns) are the same for the two compounds, the lifetime of the biradical intermediate of R-2 (200 ns) is eight times larger than that of R-1 (25 ns), explaining why diastereoselectivity is much lower in the photocyclization of R-2.

A new experimental set-up for the simultaneous, time-resolved measurement of OH and HO2 radicals by coupling high repetition rate Laser Induced Fluorescence (LIF) and cw-Cavity Ring-Down Spectroscopy (cw-CRDS) detection techniques to a laser photolysis reactor has been installed. The first experiments concern the well-known photolysis of H2O2: the absorption cross sections of H2O2 lines in the near-infrared at 6636.75 and 6639.90 cm−1 have been determined by combined results of spectroscopic and kinetic measurements of OH and HO2 radicals produced by the photolysis of H2O2 at 248 nm. These experiments will enable the measurement of absolute H2O2 concentrations in future experiments with the same set-up.

Exciplex laser photolysis at 248 and 308 nm wavelengths coupled with gas-chromatographic analysis was applied to determine the photodissociation quantum yield of acetone (QY). At 308 nm, QY has been found to decrease with decreasing temperature (T = 323–233 K) and to decrease with increasing pressure (P = 13–998 mbar synthetic air) supporting the recent suggestion that the photolysis of acetone plays a less important role in the chemistry of the upper troposphere than previously thought. Water vapour has no effect on QY in disagreement with a recent publication.

We have studied the photolysis of butenedial at 193, 248, 280, 308, 351, 400, and 450 nm by using laser photolysis combined with cavity ring-down spectroscopy. The HCO radical is a photodissociation product at 193 and 248 nm. The corresponding HCO quantum yields are 0.55 ± 0.07 and 0.12 ± 0.01, independent of butenedial pressure and nitrogen buffer gas pressure. Absorption cross-sections of butenedial are (6.88 ± 0.39) × 10−18 and (3.62 ± 0.69) × 10−19 cm2 at 193 and 248 nm. The end-products from the photolysis of butenedial at 193, 248, 308, and 351 nm were measured by FTIR. Acrolein and 3H-furan-2-one were observed and their yields have been estimated.

The binding of ligands by proteins is accompanied by rapid structural changes that are essential to function. A recent crystallographic study has revealed the ligation-linked protein motions in an allosteric protein, human hemoglobin, in both allosteric forms (T and R) upon photolysis of bound CO at cryogenic temperatures. The results show how differently the α and β subunits, within each allosteric form, respond to loss of ligand, and where the free ligand lies, establishing that the mechanism of protein control of ligand binding is radically different between the subunits.

Rate constants and other properties are reported for photochemical reactions initiated by laser photolysis (248 nm) of S2O82-(aq) in acidic solutions containing Cl-(aq) at 297 ± 2 K. The absorption spectra of SO4-•(aq) and Cl2-•(aq) are measured and compared to literature values. Equilibrium constants and rate constants involving Cl•(aq), Cl2-•(aq), H2O, SO4-•(aq), and S2O82-(aq) are determined by analyzing the formation and decay of Cl2-•(aq) and SO4-•(aq) in a self-consistent chemical mechanism. For the first time, the anticipated pH dependence is observed unambiguously in the pseudo-first-order decay rate constant of Cl2-•. The rate constants for the reactions Cl•(aq) + Cl2-•(aq) → Cl2(aq) + Cl-(aq) and Cl2-•(aq) + Cl2-•(aq) → Cl2(aq) + 2Cl-(aq) are determined; rate constants for the latter are measured as a function of temperature and ionic strength. In addition, the ionic strength dependence of the reaction SO4-•(aq) + Cl-(aq) → SO42-(aq) + Cl•(aq) is reported. Rate constants for the reactions of Cl•...

The products obtained from the ArF laser photolysis of H2CCO in the presence of a large excess of NO at T=298 K and p=3.5 mbar in He bath gas were investigated in a tubular flow reactor by time-resolved mass spectrometry. The main reaction products observed in the presence of NO were HCNO and HCN. The measured yields, ΓHCNO=0.78±0.18 and ΓHCN=0.19±0.04, respectively, were attributed to the contributions of the reactions (1a) CH 2 + NO → HCNO + H (1b) CH 2 + NO → HCN + OH and (2a) HCCO + NO → HCNO + CO (2b) ( HCCO + NO → HCN + CO 2 The time-resolved measurements are compared to results of preceding end product analyses by Fourier transform IR spectroscopy.

A new closed gas-phase system with complex oscillatory behaviour is reported. Employing the pulsed cavity ring-down technique, the absorption of static naphthalene vapour buffered with a noble gas at room temperature was measured as a function of time at 650 nm after UV multi-photon laser photolysis at 308 nm. The absorption dynamics of the static (unstirred) system exhibits extraordinary periodic and complex oscillations with periods ranging from seconds to many minutes, persisting for up to 4 h. Depending on the buffer gas pressure, several types of dynamical responses can be generated.

With near-UV Ar +-laser-induced photolysis of gaseous CH 2 I 2, efficient, large-area or localized deposition of iodine-free amorphous carbon is possible at room temperature. The method allows a separate substrate heating and thereby a tuning of the deposits properties from soft and polymer-like to diamond-like. This article reports on an observed photon–surface interaction resulting in an enhanced carbon film formation. The shape of the deposit indicates that the deposition process is supported by an increased absorption cross section of surface-adsorbed intermediate molecular fragments, with respect to flat-angle surface-impinging photons.

KrF laser-induced photolysis of gaseous (C2H5)2M (M=Se, Te) compounds is shown to be a one-photon process controlled by the cleavage of both CM bonds. It is dominated by the molecular elimination of ethene and yields elemental selenium and tellurium.

KrF laser-induced photolysis of gaseous dimethyl selenium in excess of helium is controlled by cleavage of both Se–C bonds and affords ethane as a very dominant gaseous product together with elemental selenium. The photolysis mechanism being different from that of thermolysis shows potential for chemical vapour deposition of selenium films not contaminated with carbon impurities.

We quantitatively assessed the spectroscopic changes of purple membrane in relation to the concentrations of a volatile anesthetic. As reported previously, volatile anesthetics show three modes of action on purple membrane. By using an anesthetic for which the concentration in solution could be determined spectroscopically and by applying modified analytical methods regarding the M-intermediate lifetime, we were able to clarify the quantitative relation between anesthetic concentration and each mode of action, a relation which in the past has only been described qualitatively. We also determined through the measurement of transient pH changes with pyranine that the proton pump efficiency per photochemical cycle in an action mode induced with low concentrations of anesthetic does not change from that of the native state. Moreover, we dynamically obtained the individual M−bacteriorhodopsin difference spectrum of each state at room temperature using our flash photolysis system equipped with a wavelength-tunable dye laser. These results demonstrated again that we should clearly distinguish different action modes of anesthetics according to their concentrations.

Structure effect on photochromic mechanism of 1,3,3-trimethylspiro[indoline-2,3′-[3H]naphtho[2,1,-b][1,4]oxazine] (SP1), 1,3-Dimethyl-3,2′-(1,3 -propylene)spiro[indoline-2,3′-[3H] naphtho[2,1-b][1,4]oxazine] (SP2) and 1,2′-(1,3-propylene),3,3-dimethylspiro[indo- line-2,3′ [3H]naphtho[2,1-b][1,4]oxazine](SP3) have been studied by nanosecond laser photolysis. Because of different connective positions of 1,3-propylene group in SP2 and SP3, the photochromic behaviours of them are quite different. One photoproduct of SP2 was only detected, and its lifetime is about 0.15μs. However, two colored forms of SP3 were detected after UV irradiation. The lifetimes of them are much longer than that of C-SP2. The semiempirical computational results by AM1 method were coincided with the experimental results.

Rate coefficients of reactions (1) CH3S + NO2 and (2) C2H5S + NO2 were determined using laser photolysis and laser-induced fluorescence. CH3S and C2H5S radicals were generated on photolysis of CH3SSCH3 and C2H5SSC2H5, respectively, with a KrF excimer laser at 248 nm. Their concentrations were monitored via fluorescence excited by emission from a dye laser at 371.4 nm (for CH3S) or 410.3 nm (for C2H5S) pumped with a pulsed XeCl excimer laser at 308 nm. Our measurements show that k1 (297 K) = (1.01 ± 0.15) × 10-10 cm3 molecule-1 s-1 is similar to a value reported by Balla et al. and approximately 50% greater than other previously reported values; listed errors represent 95% confidence limits. Reaction 1 has a negative activation energy: k1 = (4.3 ± 1.3) × 10-11 exp[(240 ± 100)/T] cm3 molecule-1 s-1 for T = 222−420 K. Reaction 2 has a rate coefficient similar to reaction 1 at room temperature: k2 (296 K) = (1.05 ± 0.16) × 10-10 cm3 molecule-1 s-1 but has a small positive activation energy with k2 = (2.4 ± ...

The effects of oxygen on the photochemical reactions of chromium(III) porphyrins with axial nitrogenous bases in toluene are studied by nanosecond laser flash photolysis. The photodissociation of the axial bases is confirmed to occur via both the excited states 4S1 and 6T1 (and/or 4T1) on the basis of the effect of oxygen on the quantum yield of photoreaction.

The reaction dynamics of H+H2S→H2(v, J)+SH was studied under a low-pressure bulk condition. Fast H atoms were generated by ArF laser photolysis of H2S and H2 products were detected by vacuum ultraviolet–laser-induced fluorescence (VUV–LIF) on the B 1 Σ + u – X 1 Σ + g transition. The Doppler profiles of some rotational lines of v=2 and v=3 were analyzed to determine the translational energy of H2. Although the measurements were carried out at a single geometry of the photolysis and probe lasers, the results indicate that H2 has high translational energies with narrow widths. The suggested mechanism is a direct mechanism where the H atom picks up the terminal H and SH is almost a spectator.

Chlorocobalt(III) and iodorhodium(III) tetraphenylporphyrins, (Cl)CoIIITPP and (I)RhIIITPP, react with 2,6-dimethylphenyl isocyanide (R−NC) in toluene solutions to give the isocyanide complexes, (C...

The photodissociation dynamics of jet-cooled methyl thionitrite (CH 3 SNO) have been studied using 355 nm polarised laser photolysis and probing of the NO photofragment by polarised laser-induced fluorescence. The alignment A 0 (2) between the electronic transition dipole moment involved in the absorption of the parent molecule and the rotational angular momentum J of the nascent NO ( v ″=0 and v ″=1) photofragment has been measured as a function of J up to J =44.5. The A 0 (2) values found are negative and approach the high- J limit confirming that the S 2 ←S 0 continuum transition of CH 3 SNO in the near-UV arises from a π * ←π transition to a repulsive excited state.

The mechanism of photodissociation and acid generation for three phenolic sulfonate esters, ranging from alkyl, to benzyl, to aromatic, was investigated by laser flash photolysis and product studie...

Les constantes de vitesse des reactions des atomes CI avec CH4 (k 1 ), C 2 H 6 (k 2 ), C 3 H 8 (k 3 ), et n-C 4 H 10 (k 4 ) ont ete determinees par la methode de photolyse laser pulsee-fluorescence resonante (PLP-FR). Ces reactions ont ete etudiees a temperature ambiante (297 ± 2) K et 60 Torr d'helium. Les constantes de vitesse k 2 , k 3 et k 4 ont ete mesurees en presence d'oxygene. Les valeurs obtenues sont k 1 = (1.07 ± 0.03)x100 -13 ; k 2 = (6.5 ± 0.3)x10 -11 ; k 3 = (1.31 ± 0.03)x10 -10 ; k 4 = (2.25 ± 0.06)x10 -10 (en cm 3 molecule -1 s -1 ). Ces resultats sont compares avec ceux de la litterature et constituent une validation de la methode PLP-FR recemment implantee dans notre laboratoire.

The laser photolysis of trisilane at 193 nm was studied. The final photolysis products were monosilane, disilane and tetrasilanes. The results were indicative of the participation in the photolysis process of at least two different dissociation pathways which account for about 80% of the total parent molecule dissociation. ArF laser multiphoton dissociation of Si3H8 in a free jet expansion was also studied. Photofragment fluorescence from SiH(A2Δ) and several singlet and triplet excited states of the silicon atom was observed. The rovibrational population distributions in SiH(A2Δ) were obtained by spectral simulation. The rotational distributions can be characterized by near-Boltzmann distributions. The average rotational energies in ν = 0 and ν = 1 are 1550 and 1140 cm−1 respectively and the average vibrational energy in the observed vibrational levels (ν = 0–2) is 800 cm−1., Financial support from the Spanish DGICYT (PB93-0145-CO2-01), Universidad San Pablo-CEU (project no.13/95) and the Human Capital and Mobility Programme of the European Community (CHRX-CT94-0485) is acknowledged.

Using the laser photolysis/laser-induced fluorescence (LP/LIF) pump-probe technique, the gas-phase photodissociation dynamics of room temperature HNCO was studied at a photolysis wavelength of 248 nm. H atoms produced via HNCO + hν → H(2S) + NCO(X2Π) were detected by vacuum-UV laser-induced fluorescence (VUV-LIF) at the Lyman-α transition. By means of a calibration method — using H2S photolysis as a source of well defined H atom concentrations — the absolute cross section for direct photolytic H atom formation was determined to be σH = (1.2 ± 0.3) × 10−21 cm2 molecule−1. From the H atom Doppler profiles, measured under single-collision conditions, the fraction of the available energy released as product translational energy was determined to be fT(H + NCO) = (0.55 ± 0.02). In addition, the second energetically accessible ‘spin-forbidden’ dissociation channel, HNCO + hν → NH(X3Σ−) + CO(X1Σ+), was investigated. Our results show that at a wavelength of 248 nm, direct H atom formation is the dominant dissociation channel in the HNCO photolysis.

The rate coefficients of the reactions of NCO radicals with NO and NO2: (1) NCO + NO products (293–836 K) and : (2) NCO + NO2 products (294–774 K) were measured by means of laser photolysis and laser induced fluorescence technique in the indicated temperature ranges. NCO radicals were produced from the reaction of CN, from photodissociation of ICN or BrCN, with O2. The concentration of NCO was monitored with a dye laser set at 414.95 nm. We determined k1 = 1.73 × 10−5T−2.01 exp(−470/T) cm3 molecule−1 s−1 that agrees with published results at room temperature and confirms the temperature dependence of an early report. A non-Arrhenius negative temperature dependence of k2 was observed in this work that agrees satisfactorily with results for a shock tube18 near 1250 K. We obtained k2 = 6.4 × 10−10T−0.646 exp(164/T) cm3 molecule−1 s−1 for 1250 K ≥ T ≥ 294 K by combining data of these two measurements. Our result at 294 K and the temperature dependence disagree with results of two previous investigations. © 1995 John Wiley & Sons, Inc.

Hot NH 2 radicals, which are initially generated in the ArF laser photolysis of NH 3 , relax quickly to ambient temperature in collisions with Ar. They were subsequently detected by the fluorescence of the electronically excited(NH(A 3 Π) photofragments emitting at 336 nm. The photolysis light source for the radicals was a cw Xe lamp at 147 nm. This method makes it possible to monitor NH 2 radicals for more than 0.2 s, as they slowly react with each other and diffuse out of the observation volume. The detected NH 2 concentrations ranged from≈10 13 to≈10 15 cm −3 .

Using the laser photolysis vacuum-UV laser-induced fluorescence ‘pump-and-probe’ technique, Doppler profiles of H and D atoms from the reaction O( 1 D) + HD were measured under single-collision conditions, O( 1 D) atoms were generated by laser photolysis of N 2 O at 193 nm. With a calibration method using HCl photolysis as a source of well defined H atom concentrations the following absolute rate constants k and absolute reactive cross-sections σ R have been determined: k = (1.3 ± 0.3) × 10 −10 cm 3 s −1 molec −1 and σ R (0.14 eV) = 4.0 ± 0.9 A 2 for the reaction channel O( 1 D) + HD → OD + H, and k = (1.0 ± 0.3) × 10 −10 cm 3 s −1 molec −1 and σ R (0.14 eV) = (3.0 ± 0.7) A 2 for the reaction channel O( 1 D) + HD → OH + D. The isotopic branching ratio for the reaction O( 1 D) + HD was measured directly to be Γ H/D = 1.35 ± 0.20. In addition, from the measured H and D atom Doppler profiles the fraction ƒ T of the available energy released as translational energy was determined for the individual product channels to be ƒ T (OD + H) = 0.41 ± 0.07 and ƒ T (OH + D) = 0.32 ± 0.05.

International audience; The identification of H-Rg-C5N (Rg = Kr, Xe) molecules via their IR absorption is presented. Experiments involve either UV laser photolysis of solidified rare gases doped with cyanodiacetylene (HC5N), or electrical discharges through appropriate gas mixtures, followed by the cryogenic trapping of products. Spectral assignments are based on theoretical (mainly DFT) predictions, as well as on the susceptibility of detected bands to thermal cycling and to the secondary photolysis (photobleaching).

Electronic relaxation rate constants for specific rotational levels of CH(A 2 Δ and B 2 Σ − ) have been measured. In contrast to similar measurements made earlier for other hydrides, the results obtained in the present work show an increase in the quenching efficiency upon rotational excitation. The electronically excited CH states are produced by multiphoton excitation and fragmentation of acetone upon photolysis at 193 nm by means of an ArF excimer laser light. The CG fragments are produced rotationally hot and the time evolution of rotational levels with N′ ⩽21 for CH(A 2 Δ, v′ =0) and N′ ⩽15 for CH(B 2 Σ − , v′ =0) can be measured.

Using translationally excited H atoms generated by laser photolysis of H2S at 193 nm, the reaction dynamics of H+H2O→OH+H2 and H+CO2→OH+CO was investigated at collision energies of 2.2 and 2.3 eV, respectively. Nascent OH rotational and vibrational quantum-state distributions and OH product translational energies were measured by means of the laser photolysis/laser-induced fluorescence pump-probe technique. A markedly non-statistical distribution of the available energy was found: H+H2O→OH+H2: frot=0.04±0.01, fvib

The total rate coefficients for the reactions C N + N O 2 → p r o d u c t s (1) N C O + N O 2 → p r o d u c t s (2)were measured at temperatures between 1000 and 1600 K and pressures near 1.4 atm in a shock tube. Narrow-line laser absorption was utilized to record time histories of CN and NCO radicals in C2N2/NO2/Ar laser photolysis experiments. In the experiment, CN production is nearly instantaneous via photolysis of C2N2; production of NCO radicals follows from the main product channel of reaction (1). A least-squares fit to the results for reaction (1) is given by the expression k 1 = 1.59 × 10 13 exp ⁡ ( 570 / T [ K ] ) c m 3 m o l − 1 s − 1 with corresponding uncertainty factors of f=0.91 and F=1.09 at the low-temperature extreme; f=0.84 and F=1.17 result at the high-temperature extreme. The uncertainty factors give the limiting values of the rate coefficient: kmin=fkbest fit, {itkmax=Fkbest fit. The rate coefficient of reaction (2) was measured as k2=4.5×1012 cm3 mol−1 s−1 (f=0.75, F=1.27) for temperatures near 1250 K. Incorporating the data from the present study with the results from lower-temperature studies gives the following empirical expressions for the total rate coefficients valid for temperatures ranging from 300 to 1600 K: k 1 = 6.16 × 10 15 T [ K ] − 0.752 exp ⁡ ( − 173 / T [ K ] c m 3 m o l − 1 s − 1 k 2 = 3.25 × 10 12 exp ⁡ ( 356 / T [ K ] ) c m 3 m o l − 1 s − 1 .

The vibrational and rotational state distribution and the primary quantum yield of the SO(X 3Σ−) fragment following the laser photolysis of F2SO at 193 nm have been measured by using laser-induced fluorescence spectroscopy on the SO(B 3Σ−-X 3Σ−) transition. Molecular elimination of F2 is the only energetically allowed channel to produce the SO fragment. The quantum yield measurement, Φ193 nmSO(X)=0.06±0.01, suggests that other photochemical channels, e.g. FSO+F, must be operative as well.

The chemiluminiscent reaction following the ultraviolet (266 nm) photolysis of HN 3 has been studied. A dispersed emission spectrum was recorded, which is, to the best of our knowledge, the first direct identification of the origin of the chemiluminescence. The emissive species was assigned to vibronically excited NH 2 . The observed vibrational distribution in the NH 2 (A 2 A 1 ) was not consistent with the reaction mechanism previously suggested (NH(a 1 Δ, v = 0) + HN 3 ). A modified mechanism including vibrationally excited NH(a 1 Δ) has been proposed on the basis of energetics and kinetics in terms of the emission.

Kinetics of the reactions C{sub 2}H+C{sub 2}H{sub 2}{r_arrow}C{sub 4}H{sub 2} + H (1), C{sub 2}H + H{sub 2} >C{sub 2}H{sub 2} + H (2), and C{sub 2}H + D{sub 2} {r_arrow} C{sub 2}Hd + D (3) have been studied at T=293 K with two time resolved diagnostics, laser-induced fluorescence (LIF) detection of H (or D) atoms at the Lyman-{alpha} wavelength and mass spectrometric detection of C{sub 4} H{sub 2}. The C{sub 2}H radical was prepared by the ArF (193nm) laser photolysis of C{sub 2}H{sub 2}. Measurements of the yield of H (or D) atom indicated that the C{sub 2}H radicals produced by the photolysis were converted effectively to H (or D) atoms; i.e., formation of the stable intermediates such as C{sub 4}H{sub 3} C{sub 2}H{sub 3}, or C{sub 2}HD{sub 2} was negligible under the present experimental conditions (p = 30 Torr). Rate constants of k{sub 1} = (1.6 {plus_minus} 0.1) x 10{sup {minus}10}, k{sub 2} = (7.1 {plus_minus} 1.1) x 10{sup {minus}13}, and k{sub 3} = (2.0 {plus_minus}0.3) x 10{sup {minus}13} cm{sup 3} molecular {sup {minus}1}s{sup {minus}1} were derived from the pseudo-first-order rise rates of the H (or D) atom. Rate constant of k{sub 1} = (1.4 {plus_minus} 0.3) xmore » 10{sup {minus}10} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} was also obtained at p = 5 Torr by measuring the appearance rate of C{sub 4}H{sub 2}. The ratios of the rate constants k{sub 2}/k{sub 1} = (3.4 {plus_minus} 0.2) x 10{sup {minus}3} and K{sub 3}/K{sub 1} = (1.4 {plus_minus}0.5) x 10{sup {minus}3} were deduced by measuring the dependence of the C{sub 4}H{sub 2} production on the partial pressure of added H{sub 2} or D{sub 2}. Transition state theory calculations on the basis of ab initio transition-state properties demonstrated the importance of the tunnel effect of reaction 2 at room temperature. 27 refs., 8 figs., 2 tabs.« less

The photolysis by laser radiation (488 nm) of Kr, Xe, O 2 and UF 5 dissolved in liquid fluorine affords KrF 2 , XeF 2 , O 4 F 2 or O 2 F 2 , and UF 6 , respectively. No reaction product was observed on laser photolysis of liquid fluorine with Ar, N 2 , IF 5 , RuF 5 or OsF 6 .

The time resolved polarized CARS technique has been used to detect Cl atoms produced by photolysis of ICl in the presence and absence of O2. A population inversion was observed between the ground state electronic levels Cl(2P1/2) and Cl(2P3/2). The rate constant for Cl(2P1/2) decay (quenching + reaction) in ICl was determined to be (3.2±0.2)×10−13 cm3/molecule×s; the rate constant for Cl(2P3/2) reaction with ICl was determined to be (7.8±0.5)×10−12 cm3/molecule×s; and the rate constant for Cl(2P1/2) quenching by O2 was determined to be (1.9±0.2)×10−13 cm3/molecule×s.

A technique combining the fluorescence and time-resolved CIDEP of free radicals in solution was developed for laser photolysis studies. The potential of this powerful technique is applied to the photolysis of the anthraquinone/organosilane system with both the ESR and fluorescence results clearly attributed to the semi-anthraquinone-silyl radicals.

NH(a1Δ, v″ ≤ 3) was produced in a quasi-static exciplex laser photolysis cell from the photodissociation of HN3 at λL = 248 nm. Undispersed laser-induced excitation spectra of the transitions NH(c1Π)-(a1Δ) (0-2) and (0-3) were recorded to determine the band origins ν 02 and ν 03 , ν 02 = 24 484.61 ± 0.1 cm -1 ν 03 = 32 6+2.60 ± 0.07 cm -1 ; the vibrational constants ωe, ωeχe, and ωeγe, ω e = 3331.15 ± 0.40 cm -1 ω e χ e = 74.84 ± 0.30 cm -1 ω e γ e = 0.40 ± 0.06 cm -1 ; and the rotational constants BΔ, DΔ, and HΔ of the (a1Δ) state, B Δ (ν″ =2) = 15.203 ± 0.002 cm -1 D Δ (ν″ =2) = (1.61 ± 0.03)· 10 -3 cm -1 H Δ (ν″ =2) = (0.9 ± 0.07)· 10 -7 cm -1 B Δ (ν″ =3) = 14.599 ± 0.003 cm -1 D Δ (ν″ =3) = (1.56 ± 0.06)· 10 -3 cm -1 . These spectroscopic constants are compared to the values available in the literature.

The yield of CO from CH 2 (a 1 A 1 ) + CH 2 CO has been measured by monitoring the transient IR absorption of carbon monoxide following pulsed laser photolysis of ketene (CH 2 CO + hv (308 nm) → CH 2 (a 1 A 1 ) + CO). Analysis of the prompt CO production as a function of CH 2 (a 1 A 1 ) scavenger concentration ([ i -C 4 H 8 ] and [N 2 ]) gives a CO yield of 0.63 ± 0.13, which suggests that collision-induced intersystem crossing (CH 2 (a 1 A 1 ) + CH 2 CO → CH 2 (X 3 B 1 ) + CH 2 CO) is important in this reaction.

The paper offers and substantiates a technique for quantitative processing of the photochemical reactions in polynucleotides, nucleoproteins and their components caused by the action of powerful ultraviolet laser pulse radiation.

The development and first tests of a novel method for the direct, sensitive, selective, and fast detection of gaseous nitric acid in air are described. The detection method is based on the laser-photolysis fragment-fluorescence (LPFF) method using 193 nm (ArF) laser light. The photolysis process yielding OH fluorescence has been thoroughly investigated. Up to now, the method has been found to be practically free of interferences. The mixing ratio for nitric acid is measured on-line with a detection limit of about 0.1 ppbv for an accumulation time of the signal of 10–15 min. A number of tests and field measurements were performed to demonstrate the feasibility and limits of the described detection method.

Photochemistry of ax,ax-L(OC) 4 Mn-Mn(Co) 4 L (L=P(n-Bu) 3 ) (S) in cyclohexane has been studied by means of laser photolysis with a uv-vis detection system. In addition to the transient absorption features due to the occurrence of primary processes, (1) Mn-Mn bond cleavage to give (Mn(CO) 4 L (I), and 2) CO dissociation without metal-metal bond cleavage to give Mn 2 (CO) 7 L 2 (II). Two absorption features are observed: The one is attributed to the formation of a secondary intermediate (IV), whose structure is assigned to ax,eq-L(OC) 4 Mn-Mn(CO) 4 L, from the reaction of II with CO. The other appears to show the possibility of a third primary process (3) in the photolysis system of the disubstituted L(OC) 4 Mn-Mn(CO) 4 L. A whole photochemical reaction scheme is proposed in Scheme 2 and the nature of the intermediates, IV and unknown II is discussed.