vacuum-UV Laser-induced Fluorescence Research Articles

Pulsed laser photolysis vacuum UV laser-induced fluorescence kinetic study of the reactions of Cl( 2P 3/2) atoms with ethyl formate, n-propyl formate, and n-butyl formate

Cl( 2P 3/2) atoms were produced by photolysis of Cl 2 at 351 nm in the presence of alkyl formates and monitored by LIF spectroscopy at 134.72 nm. Rate coefficients of k(Cl + C 2H 5OC(O)H) = (9.5 ± 0.3)×10 −12, k(Cl + n-C 3H 7OC(O)H) = (4.5 ± 0.3) × 10 −11 and k(Cl + n-C 4H 9OC(O)H) = (1.2 ± 0.1) × 10 −10 cm 3 molecule −1 s −1 were determined at 295 ± 2 K in 6–7 Torr of Ar diluent. These values are 15–30% lower than reported in a previous pulsed laser photolysis resonance fluorescence study. The discrepancy may reflect complications arising from the fact that the time scales for chlorine atom loss and regeneration were not sufficiently decoupled in the previous study.

Vacuum UV laser-induced fluorescence study of the collisional removal of Br( 2P 1/2) atoms by small molecules

This Letter reports on the application of the vacuum ultraviolet laser-induced fluorescence detection of Br( 2P 1/2) atoms at 157.48 nm to the kinetic study of collisional removal of Br( 2P 1/2) by small molecules at 295 K. Gas mixtures of a small amount of CH 3Br and an excess amount of collision partners are exposed to pulsed laser irradiation at 193 nm. Temporal decay profile of the Br∗ LIF intensity has been monitored to determine the collisional removal rate coefficients. The collision partners are H 2, CO 2, CF 4, CF 2H 2, H 2O, CH 3OH, and SF 5CF 3, and the results are compared to literature data.

Pulsed Laser Photolysis Vacuum UV Laser-Induced Fluorescence Kinetic Study of the Gas-Phase Reactions of Cl(2P3/2) Atoms with C3−C6 Ketones

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionPulsed Laser Photolysis Vacuum UV Laser-Induced Fluorescence Kinetic Study of the Gas-Phase Reactions of Cl(2P3/2) Atoms with C3−C6 KetonesKenshi Takahashi, Erika Iwasaki, Yutaka Matsumi, and Timothy J. WallingtonCite this: J. Phys. Chem. A 2007, 111, 32, 8044–8045Publication Date (Web):July 10, 2007Publication History Published online10 July 2007Published inissue 1 August 2007https://doi.org/10.1021/jp074638+Copyright © 2007 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views227Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (15 KB) Get e-Alerts Get e-Alerts

Pulsed Laser Photolysis Vacuum UV Laser-Induced Fluorescence Kinetic Study of the Gas-Phase Reactions of Cl(2P3/2) Atoms with C3−C6 Ketones

The gas-phase reactions of Cl atoms with acetone, butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, and cyclopentanone at 295 +/- 2 K were studied using pulsed laser photolysis vacuum UV laser-induced fluorescence (PLP-LIF) techniques. Cl(2P(3/2)) atoms were produced by photolysis of Cl2 at 351 nm and monitored by LIF spectroscopy at 134.72 nm (3p(5) 2P(3/2)-3p(4)4s 2P(3/2) transition). Rate coefficients for reactions of Cl atoms with acetone, butanone, 2-pentanone, 3-pentanone, 2-hexanone, 3-hexanone, and cyclopentanone are (2.30 +/- 0.12) x 10(-12), (4.08 +/- 0.21) x 10(-11), (1.23 +/- 0.13) x 10(-10), (8.87 +/- 0.92) x 10(-11), (2.08 +/- 0.32) x 10(-10), (1.43 +/- 0.19) x 10(-10) and (1.16 +/- 0.12) x 10(-10) cm3 molecule(-1) s(-1), respectively. The results for acetone and butanone are consistent with previous studies. The results for 2-pentanone, 3-pentanone, 2-hexanone, and 3-hexanone are approximately a factor of 2-3 higher than those from previous absolute rate studies. Likely explanations for these discrepancies are discussed. Tropospheric lifetimes of ketones with respect to reaction with Cl atoms are estimated and discussed.

Accurate Determination of the Absolute Quantum Yield for O(1D) Formation in the Photolysis of Ozone at 308 nm.

For Abstract see ChemInform Abstract in Full Text.

Accurate Determination of the Absolute Quantum Yield for O(1D) Formation in the Photolysis of Ozone at 308 nm

Absolute O('D) quantum yield from the photodissociation reaction of O 3 at 308 nm should be determined accurately with high precision for its atmospheric significance. This is because it has been used as a reference in previous relative measurements to obtain the O( 1 D) quantum yields as a function of photolysis wavelength in the near-UV region. In this study, the near-UV pulsed-laser photolysis of O 3 with the direct detection of the O( 1 D) and O( 3 P) photofragments using a technique of vacuum UV laser-induced fluorescence has been applied to determine the absolute O('D) quantum yield from O 3 photolysis. The absolute O( 1 D) quantum yield at 308.0 nm at room temperature (298 ′ 2 K) is determined to be 0.804 ′ 0.048 (95% confidence interval), in which the uncertainty is much smaller than the values recommended for use in atmospheric studies. The O( 1 D) quantum yield values at photolysis wavelengths between 307 and 311.5 nm are also presented.

A vacuum-UV laser-induced fluorescence experiment for measurement of rotationally and vibrationally excited H2

An experimental setup is built to detect spatially resolved rovibrationally excited hydrogen molecules via laser-induced fluorescence. To excite the hydrogen molecules, laser radiation is produced in the vacuum UV part of the spectrum. The laser radiation is tunable between 120 nm and 230 nm and has a bandwith of 0.15 cm−1. The wavelength of the laser radiation is calibrated by simultaneous recording of the two-photon laser induced fluorescence spectrum of nitric oxide. The excited hydrogen populations are calibrated on the basis of coherent anti-Stokes Raman scattering measurements. A population distribution is measured in the shock region of a pure hydrogen plasma expansion. The higher rotational levels (J>5) show overpopulation compared to a Boltzmann distribution determined from the lower rotational levels (J⩽5).

Photodissociation dynamics of HNCO at 248 nm

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( 2 S) + NCO( X 2Π) were detected by vacuum-UV laser-induced fluorescence (VUV-LIF) at the Lyman-α transition. By means of a calibration method — using H 2S photolysis as a source of well defined H atom concentrations — the absolute cross section for direct photolytic H atom formation was determined to be σ H = (1.2 ± 0.3) × 10 −21 cm 2 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 f T(H + NCO) = (0.55 ± 0.02). In addition, the second energetically accessible ‘spin-forbidden’ dissociation channel, HNCO + hν → NH( X 3Σ −) + CO( X 1Σ +) , 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.

Insertion vs. Abstraction in the Reactions of NH(a1Δ, v = 0, 1) with H2 and D2

Abstract Gas-phase reactions of NH(a1Δ, v = 0,1) + H2 (1) and NH(a1Δ, v = 0,1) + D2 (2) were studied in the photolysis of HNCO/H2 (or D2) mixtures. NH(a1Δ) and product H (D) atom were detected by UV and vacuum-UV laser-induced fluorescence. The observed rate constants at room temperature (295 ± 2K) and activation energies in the range of 295 — 407 K were; in units of 10−12 cm3 molecule−1 s−1 and kJ mol−1. The product branching ratio in reaction 2 was determined to be [D]/[H] = 3.2 ± 0.76, in which no temperature dependence was indicated. These results are consistent with insertion mechanism having a loose entrance transition state structure, which is suggested by ab initio CI calculations. In contrast, the contribution of direct abstraction channel is supposed to be negligibly small.

Absolute reactive cross sections for the reaction OH+CO→H+CO 2

Using laser photolysis and vacuum-UV laser-induced fluorescence “pump-and-probe” technique, the microscopic dynamics of the reaction OH+CO→H+CO 2 was studied at different center of mass energies. Translationally excited OH radicals were generated by laser photolysis of H 2 O 2 at a wavelength of 248 nm and 193 nm, and the nascent H atoms produced in the reaction of OH with room temperature CO molecules were detected under single collision conditions by vacuum-UV laser-induced fluorescence at the Lyman-α transition. With a calibration method using H 2 S (248 nm) and HCl (193 nm) photolysis as a source of well-defined H atom concentrations, the following absolute reaction cross sections were measured: δ R (0.82 eV)=(0.3±0.1) 2 and δ R (1.13 eV)=(1.2±0.3) 2 . The experimental results are compared with full-dimensional (6D) quasiclassical trajectory studies carried out using a global potential energy surface, derived from ab initio calculations.

Absolute rate constants, reactive cross-sections and isotopic branching ratio for the reaction of O( 1D) with HD

Using the laser photolysis vacuum-UV laser-induced fluorescence ‘pump-and-probe’ technique, Doppler profiles of H and D atoms from the reaction O( 1D) + HD were measured under single-collision conditions, O( 1D) atoms were generated by laser photolysis of N 2O 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 3s −1 molec −1 and σ R(0.14 eV) = 4.0 ± 0.9 Å 2 for the reaction channel O( 1D) + 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) Å 2 for the reaction channel O( 1D) + HD → OH + D. The isotopic branching ratio for the reaction O( 1D) + 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.

Ultraviolet photodissociation dynamics of carbon suboxide

The vibrational and rotational excitation of CO produced in the UV laser photodissociation of carbon suboxide, C 3O 2, has been investigated. The internal energy of CO was detected under collision-free conditions by means of a pulsed vacuum UV laser probe, employing a two-laser time-resolved approach. The C 3O 2 was photodissociated at 266, 248, and 193 nm. The CO photoproduct was found to be vibrationally and rotationally excited as compared with a room temperature thermal equilibrium CO distribution. The average rotational energy and vibrational energy of the CO were determined to be 1.9 ± 0.2 kcal mol −1 and 0.6 ± 0.2 kcal mol −1 respectively at 266 nm, 2.6 ± 0.1 kcal mol −1 and 2.0 ± 0.5 kcal mol −1 at 248 nm, and 2.8 ± 0.2 kcal mol −1 and 1.4 ± 0.6 kcal mol −1 at 193 nm. Statistical calculation assuming C 3O 2 → CO + C 2O predicted substantially greater internal excitation in CO than was obtained experimentally. The CO internal energy increased with excitation wavelength; it could be crudely described by an impulsive model. The carbon atoms produced by the 193 nm photolysis of C 3O 2 were also probed by vacuum UV laser-induced fluorescence. Only ground state C( 3P J ) was detected. The branching ratio between carbon atom and C 2O radical formation following 193 nm excitation of C 3O 2 was found to be 6% ± 3%.

T 1 barrier height, S1–T1 intersystem crossing rate, and S0 radical dissociation threshold for H2CO, D2CO, and HDCO

Vacuum UV laser-induced fluorescence has been used to detect the atomic products in the photofragmentation of H2CO, D2CO, and HDCO. The dissociation is shown to occur on both the ground (S0) and the first triplet (T1) potential surfaces. The T1 exit barrier height (2.9–6.0 kcal/mol) and the S1→T1 intersystem crossing rate near the T1 barrier top (4×107 s−1) have been determined experimentally. The threshold energy for the radical dissociation channel on the S0 surface, 86.57±0.16 kcal/mol, has also been measured accurately by rovibronically resolved photolysis. The best values for the heat of formation (9.99±0.19 kcal/mol) and the C–H bond enthalpy (15.69±0.19 kcal/mol) of HCO radical have been derived from the measured threshold energies as well.

Photofragmentation dynamics of ketene at 308 nm: Initial vibrational and rotational state distributions of CO product by vacuum UV laser-induced fluorescence

The vibration-rotation state distribution of CO(v,J) from CH2CO flash photolysis at 308 nm has been determined by pulsed VUV laser-induced fluorescence. The excited ketene molecule appears to internally convert to vibrationally excited ground singlet state and to dissociate on that surface, CH2CO+308 nm→CH2(1A1)+CO+6.7 kcal/mol. There are no energetic CO molecules which would indicate formation of the lower energy CH2 triplet state. The observed rotational distributions of CO(v=0) and CO(v=1) are roughly matched by rotational temperatures of 1300 and 550 K, respectively; the data are accurately matched by phase space theory (PST). PST assumes that all energetically accessible product states have equal probability; it contains no adjustable parameters. PST predicts the ratio of v=1 to v=0 populations to be 0.013 compared to an observed value of 0.09±0.05. A Franck–Condon calculation gives too much vibrational excitation, 0.22±0.07. The separate statistical ensemble (SSE) model of Wittig which decouples overall ketene rotation from the other internal degrees of freedom gives 0.082 in agreement with experiment. This type of statistical distribution is likely to characterize bond fissions for which the barrier is just the dissociation limit itself.