Time-resolved Fourier-transform Spectroscopy Research Articles

Investigation of Electronic Structures of Triplet States Using Step-Scan Time-Resolved Fourier-Transform Near-Infrared Spectroscopy.

Triplet transitions of light-emitting materials, including rose bengal, tris(2-phenylpyridine)iridium(III) [Ir(ppy)3], tris(1-phenylisoquinoline)iridium(III) [Ir(piq)3], and bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic), were studied using step-scan time-resolved Fourier-transform near-infrared spectroscopy. The samples were excited to their singlet excited states by a 355 nm laser and then underwent efficient conversions/crossings to their triplet manifolds. For rose bengal, a transient absorption band appeared at 9400 cm-1, attributed to the T3 ← T1 transition based on the corresponding time evolution and the theoretical calculations. For Ir(ppy)3, Ir(piq)3, and FIrpic, the most intense bands were observed at 7700, 7500, and 7500 cm-1 and assigned to T7 ← T1, T6 ← T1, and T6 ← T1 transitions, respectively. For Ir(ppy)3, the most intense band involved transitions between different triplet metal-to-ligand charge transfer (3MLCT) states, while for Ir(piq)3 and FIrpic, they involved a metal center to 3MLCT transition. These T1 states were assigned to 3MLCT.

Effect of flue gas temperature on NO2 adsorption by aged recycled concrete Waste: DRIFTS, TGA and BET study

Removing NO2 from cement kilns can have tremendously beneficial effects on the environment and human health. Sequestering NO2 in demolished concrete is an innovative, cost-effective, and sustainable approach to remove NO2 flue-gas from cement kilns and other industrial plants to minimize their environmental impact. Another notable advantage of this approach was signified by our recent discovery of NO2 sequestered Recycled Concrete Aggregate (NRCA) acting as a corrosion inhibitor when recycled backed into new concrete. This paper focuses on NO2 sequestration by the waste concrete at elevated temperatures that are representative of those found in the cement kilns flue gas exhaust. The gas-phase uptake experiments were performed for 1, 2, and 20-years old concrete samples to reflect the variable age of NRCA. The mechanistic studies of NO2 adsorption to concrete surfaces at 27 °C, 150 °C, and 250 °C temperatures that simulate flue gas temperatures were obtained by time-resolved Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs) and gas-phase analysis. The results showed that NO2 sequestration increased with an increase in temperature. Most importantly, the 20-year-old concrete still had significant uptake capacity, which shows that aged waste concrete can be used to reduce air pollution and then recycled back into new concrete structures to prevent corrosion. These findings were also supported by TGA, BET, and XRD results. The XRD data indicated a presence of alite, belite, ettringite, portlandite, and dolomite, where the increased fractions of portlandite and hydrates were correlated to higher NO2 uptake. Moreover, the BET results indicated notable changes in the microstructure of the concrete at elevated temperatures, which also contributed to changes in the NO2 uptake capacity of concrete.

CO2 methanation and reverse water gas shift reaction. Kinetic study based on in situ spatially-resolved measurements

The reaction kinetics for the CO2 methanation and reverse water gas shift reaction over an ordered-mesoporous Ni/Al2O3 catalyst were determined. For the parameter estimation and model discrimination, the kinetic data were obtained by means of spatially-resolved measurement in a catalytic plate reactor. In detail, ~21,000 high-resolution gas composition data were gathered along the reactor axis using a movable sampling capillary connected to a mass spectrometer. Additionally, the catalyst surface temperature was determined via infrared thermography. The influence of reaction temperature (320–420 °C), total pressure (1.2–7.3 barabs), and GHSV, as well as possible inhibition of products such as CH4 and H2O, were investigated.A one-dimensional model of the reactor was developed describing the conservation of mass in the bulk gas and catalyst phase. The Bayesian approach was used to estimate the kinetic parameters of 20 proposed Langmuir-Hinshelwood rate expressions for the CO2 methanation that were derived based on three different mechanisms (i.e., direct dissociation, hydrogen assisted dissociation, and hybrid mechanism). Two kinetic models reflected the measured data very well. The most probable models suggest that the rate determining step includes the reaction of an oxygenated complex (COH* or HCOO*) with an active site (*) or an adsorbed hydrogen (H*). Furthermore, water was assumed to be adsorbed as a hydroxyl species (OH*), while methane did not influence the reaction. Temperature- and time-resolved Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) measurements confirmed the presence of both adsorbed surface intermediates.

Does Tetrahydrofuran (THF) Behave like a Solvent or a Reactant in the Photolysis of Thionyl Chloride (Cl2SO) in Cyclohexane? A Transient Infrared Difference Study.

The photolysis of thionyl chloride (Cl2SO) in pure cyclohexane (cHex) and in cHex with a small amount of tetrahydrofuran (THF) irradiated with 266 nm pulsed laser was investigated using time-resolved step-scan Fourier-transform spectroscopy. The density functional theory B3LYP, with the conductor-like polarizable continuum model to account for the effects of solvents, was employed to predict the molecular parameters of the relevant species. Monitoring the wavenumbers and infrared absorbances attributed to the [S,O] species and accounting for the stoichiometry revealed SO2 to be the major oxygen-containing end product for the thermal decomposition of Cl2SO. Upon successive irradiation with 266 nm pulsed laser, the major product, as detected by IR absorption, was S2O with minor SO3, which could be generated from the secondary reactions of the photolytic intermediate ClSO. The majority of the transient vibrational features upon 266 nm irradiation of the mixture of Cl2SO/cHex was attributed to ClSO, characterized at 1155 cm-1, coupled with a minor contribution of (ClSO)2 at 1212 and 1173 cm-1. For the mixture of Cl2SO/THF/cHex, the transient population of ClSO was retained, but the amount of (ClSO)2 was slightly reduced, coupled with a new upward feature at 1054 cm-1 that was plausibly attributed to the C-O-C asymmetric stretching mode of ClSO-THF complex. Upon the successive irradiation of the Cl2SO/THF/cHex mixture, the amount of S2O was also decreased. The observed complexes of THF with solutes suggested that THF should not be merely treated as a solvent but regarded as a coordination molecule in organic synthesis. The formation of the intermediate-THF complexes altered the reaction pathways, as well as the types and populations of the end products.

Observing the Formation and the Reactivity of an Octahedral Iron(V) Nitrido Complex in Real Time

Give me five: Time-resolved Fourier-transform IR spectroscopy is used to time-resolve the formation and the reaction dynamics of a fourfold symmetrical nitrido iron(V) complex (light blue C, red Fe, blue N) in liquid solution under physiological and technologically relevant conditions.

Dynamics of the reactions of O(1D) with CD3OH and CH3OD studied with time-resolved Fourier-transform IR spectroscopy

We investigated the reactivity of O((1)D) towards two types of hydrogen atoms in CH(3)OH. The reaction was initiated on irradiation of a flowing mixture of O(3) and CD(3)OH or CH(3)OD at 248 nm. Relative vibration-rotational populations of OH and OD (1 ≤ v ≤ 4) states were determined from their infrared emission recorded with a step-scan time-resolved Fourier-transform spectrometer. In O((1)D) + CD(3)OH, the rotational distribution of OD is nearly Boltzmann, whereas that of OH is bimodal; the product ratio [OH]/[OD] is 1.56 ± 0.36. In O((1)D) + CH(3)OD, the rotational distribution of OH is nearly Boltzmann, whereas that of OD is bimodal; the product ratio [OH]/[OD] is 0.59 ± 0.14. Quantum-chemical calculations of the potential energy and microcanonical rate coefficients of various channels indicate that the abstraction channels are unimportant and O((1)D) inserts into the C-H and O-H bonds of CH(3)OH to form HOCH(2)OH and CH(3)OOH, respectively. The observed three channels of OH are consistent with those produced via decomposition of the newly formed OH or the original OH moiety in HOCH(2)OH or decomposition of CH(3)OOH. The former decomposition channel of HOCH(2)OH produces vibrationally more excited OH because of incomplete intramolecular vibrational relaxation, and decomposition of CH(3)COOH produces OH with greater rotational excitation, likely due to a large torque angle during dissociation. The predicted [OH]/[OD] ratios are 1.31 and 0.61 for O((1)D) + CD(3)OH and CH(3)OD, respectively, at collision energy of 26 kJ mol(-1), in satisfactory agreement with the experimental results. These predicted product ratios vary weakly with collision energy.

Atomic cesium 6h states observed by time-resolved FTIR spectroscopy

The infrared emission spectra of Cs resulting from the laser ablation of CsI tablets in a vacuum were recorded using time-resolved Fourier-transform spectroscopy in the 1200–1600 cm−1 range with a resolution of 0.017 cm−1. The 6h level of Cs was observed. The probabilities of transitions between the observed levels are calculated.

Low-excited f-, g- and h-states in Au, Ag and Cu observed by Fourier-transform infrared spectroscopy in the 1000–7500 cm−1 region

The infrared emission spectra of Au, Ag and Cu resulting from the laser ablation of metal targets in a vacuum were recorded using time-resolved Fourier-transform spectroscopy in the 1200–1600, 1900–3600, 4100–5000 and 5200–7500 cm−1 ranges with a resolution of 0.017 cm−1. The majority of the observed lines correspond to transitions between low-excited Rydberg (Nd10)nlj states of Cu (N = 3), Ag (N = 4) and Au (N = 5) with a principal quantum number n = 4, …, 10; the most prominent lines being due to transitions between the states with high orbital momenta l = 3, …, 5. This study reports 32 new lines of Au, 12 of Ag and 20 of Cu (with uncertainties of 0.0003–0.03 cm−1). From the lines observed here and in our previous works, we extract revised energy values for 85 energy levels (uncertainty 0.01–0.03 cm−1) of which eight levels of Au, three of Ag and four of Cu are reported for the first time. These newly reported levels have high orbital momentum l = 3, 4, 5.

Infrared absorption of CH3OSO detected with time-resolved Fourier-transform spectroscopy

A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to detect temporally resolved infrared absorption spectra of CH(3)OSO produced upon irradiation of a flowing gaseous mixture of CH(3)OS(O)Cl in N(2) or CO(2) at 248 nm. Two intense transient features with origins near 1152 and 994 cm(-1) are assigned to syn-CH(3)OSO; the former is attributed to overlapping bands at 1154 ± 3 and 1151 ± 3 cm(-1), assigned to the S=O stretching mixed with CH(3) rocking (ν(8)) and the S=O stretching mixed with CH(3) wagging (ν(9)) modes, respectively, and the latter to the C-O stretching (ν(10)) mode at 994 ± 6 cm(-1). Two weak bands at 2991 ± 6 and 2956 ± 3 cm(-1) are assigned as the CH(3) antisymmetric stretching (ν(2)) and symmetric stretching (ν(3)) modes, respectively. Observed vibrational transition wavenumbers agree satisfactorily with those predicted with quantum-chemical calculations at level B3P86∕aug-cc-pVTZ. Based on rotational parameters predicted at that level, the simulated rotational contours of these bands agree satisfactorily with experimental results. The simulation indicates that the S=O stretching mode of anti-CH(3)OSO near 1164 cm(-1) likely makes a small contribution to the observed band near 1152 cm(-1). A simple kinetic model of self-reaction is employed to account for the decay of CH(3)OSO and yields a second-order rate coefficient k=(4 ± 2)×10(-10) cm(3)molecule(-1)s(-1).

Time-resolved FTIR emission spectroscopy of Cu in the 1800–3800 cm−1 region: transitions involving f and g states and oscillator strengths

Time-resolved Fourier-transform spectroscopy was applied to the study of the emission spectra of Cu vapours in a vacuum (10−2 Torr) produced in ablation of a Cu metal target by a high-repetition rate (1.0 kHz) pulsed nanosecond ArF laser (λ = 193 nm, output energy of 15 mJ). The time-resolved infrared emission spectrum of Cu was recorded in the 1800–3800 cm−1 spectral region with a resolution of 0.017 cm−1. The time profiles of the measured lines have maxima at 18–20 µs after a laser shot and display non-exponential decay with a decay time of 5–15 µs. This study reports 17 lines (uncertainty 0.0003–0.018 cm−1) of Cu I not previously observed. This results in seven newly-found levels and revised energy values for 11 known levels (uncertainty 0.01–0.03 cm−1). We also calculate transition probabilities and oscillator strengths for several transitions involving the reported Cu levels.

Internal energy of HCl upon photolysis of 2-chloropropene at 193 nm investigated with time-resolved Fourier-transform spectroscopy and quasiclassical trajectories

Following photodissociation of 2-chloropropene (H(2)CCClCH(3)) at 193 nm, vibration-rotationally resolved emission spectra of HCl (upsilon < or = 6) in the spectral region of 1900-2900 cm(-1) were recorded with a step-scan time-resolved Fourier-transform spectrometer. All vibrational levels show a small low-J component corresponding to approximately 400 K and a major high-J component corresponding to 7100-18,700 K with average rotational energy of 39+/-(3)(11) kJ mol(-1). The vibrational population of HCl is inverted at upsilon = 2, and the average vibrational energy is 86+/-5 kJ mol(-1). Two possible channels of molecular elimination producing HCl + propyne or HCl + allene cannot be distinguished positively based on the observed internal energy distribution of HCl. The observed rotational distributions fit qualitatively with the distributions of both channels obtained with quasiclassical trajectories (QCTs), but the QCT calculations predict negligible populations for states at small J. The observed vibrational distribution agrees satisfactorily with the total QCT distribution obtained as a weighted sum of contributions from both four-center elimination channels. Internal energy distributions of HCl from 2-chloropropene and vinyl chloride are compared.

Photodissociation Dynamics of Phenol

The photodissociation of phenol at 193 and 248 nm was studied using multimass ion-imaging techniques and step-scan time-resolved Fourier-transform spectroscopy. The major dissociation channels at 193 nm include cleavage of the OH bond, elimination of CO, and elimination of H(2)O. Only the former two channels are observed at 248 nm. The translational energy distribution shows that H-atom elimination occurs in both the electronically excited and ground states, but elimination of CO or H(2)O occurs in the electronic ground state. Rotationally resolved emission spectra of CO (1 <or= v <or= 4) in the spectral region of 1860-2330 cm(-1) were detected upon photolysis at 193 nm. After a correction for rotational quenching, CO (v <or= 4) shows a nascent rotational temperature of approximately 4600 K. The observed vibrational distribution of (v = 1)/(v = 2)/(v = 3)/(v = 4) = 64.3/22.2/9.1/4.4 corresponds to a vibrational temperature of 3350 +/- 20 K. An average rotational energy of 6.9 +/- 0.7 kcal mol(-1) and vibrational energy of 3.8 +/- 0.7 kcal mol(-1) are observed for the CO product. The dissociation channels, translational energy distributions of the photofragment, and vibrational and rotational energies of product CO are consistent with potential energy surfaces from quantum chemical calculations and the branching ratios from an RRKM calculation.

Infrared absorption of gaseous ClCS detected with time-resolved Fourier-transform spectroscopy

A transient infrared absorption spectrum of gaseous ClCS was detected with a step-scan Fourier-transform spectrometer coupled with a multipass absorption cell. ClCS was produced upon irradiating a flowing mixture of Cl2CS and N2 or CO2 with a KrF excimer laser at 248 nm. A transient band in the region of 1160-1220 cm-1, which diminished on prolonged reaction, is assigned to the C-S stretching (nu1) mode of ClCS. Calculations with density-functional theory (B3P86 and B3LYP/aug-cc-pVTZ) predict the geometry, vibrational wave numbers, and rotational parameters of ClCS. The rotational contour of the spectrum of ClCS simulated based on predicted rotational parameters agrees satisfactorily with experimental observation; from spectral simulation, the band origin is determined to be at 1194.4 cm-1. Reaction kinetics involving ClCS, CS, and CS2 are discussed.

Infrared absorption of C6H5SO2 detected with time-resolved Fourier-transform spectroscopy

C6H5SO2 radicals were produced upon irradiation of three flowing mixtures: C6H5SO2Cl in N2, C6H5Cl and SO2 in CO2, and C6H5Br and SO2 in CO2, with a KrF excimer laser at 248 nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record the time-resolved infrared (IR) absorption spectra of reaction intermediates. Two transient bands with origins at 1087.7 and 1278.2 cm-1 are assigned to the SO2-symmetric and SO2-antisymmetric stretching modes, respectively, of C6H5SO2. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predict the geometry and vibrational wave numbers of C6H5SO2 and C6H5OSO. The vibrational wave numbers and IR intensities of C6H5SO2 agree satisfactorily with the observed new features. Rotational contours of IR spectra of C6H5SO2 simulated based on predicted molecular parameters agree satisfactorily with experimental results for both bands. The SO2-symmetric stretching band is dominated by a- and c-type rotational structures and the SO2-antisymmetric stretching band is dominated by a b-type rotational structure. When C6H5SO2Cl was used as a precursor of C6H5SO2, C6H5SO2Cl was slowly reproduced at the expense of C6H5SO2, indicating that the reaction Cl+C6H5SO2 takes place. When C6H5Br/SO2/CO2 was used as a precursor of C6H5SO2, features at 1186 and 1396 cm-1 ascribable to C6H5SO2Br were observed at a later period due to secondary reaction of C6H5SO2 with Br. Corresponding kinetics based on temporal profiles of observed IR absorption are discussed.

Distribution of Internal States of CO from O (1D) + CO Determined with Time-Resolved Fourier Transform Spectroscopy

Following collisions of O (1D) with CO, rotationally resolved emission spectra of CO (1 < or = v < or = 6) in the spectral region 1800-2350 cm(-1) were detected with a step-scan Fourier transform spectrometer. O (1D) was produced by photolysis of O3 with light from a KrF excimer laser at 248 nm. Upon irradiation of a flowing mixture of O3 (0.016 Torr) and CO (0.058 Torr), emission of CO (v < or = 6) increases with time, reaches a maximum approximately 10 micros. At the earliest applicable period (2-3 micros), the rotational distribution of CO is not Boltzmann; it may be approximately described with a bimodal distribution corresponding to temperatures approximately 8000 and approximately 500 K, with the proportion of these two components varying with the vibrational level. A short extrapolation from data in the period 2-6 micros leads to a nascent rotational temperature of approximately 10170 +/- 600 K for v = 1 and approximately 1400 +/- 40 K for v = 6, with an average rotational energy of 33 +/- 6 kJ mol(-1). Absorption by CO (v = 0) in the system interfered with population of low J levels of CO (v = 1). The observed vibrational distribution of (v = 2):(v = 3):(v = 4):(v = 5):(v = 6) = 1.00:0.64:0.51:0.32:0.16 corresponds to a vibrational temperature of 6850 +/- 750 K. An average vibrational energy of 40 +/- 4 kJ mol(-1) is derived based on the observed population of CO (2 < or = v < or = 6) and estimates of the population of CO (v = 0, 1, and 7) by extrapolation. The observed rotational distributions of CO (1 < or = v < or = 3) are consistent with results of previous experiments and trajectory calculations; data for CO (4 < or = v < or = 6) are new.

Infrared absorption of CH3SO2 detected with time-resolved Fourier-transform spectroscopy

A step-scan Fourier-transform spectrometer coupled with a 6.4 m multipass absorption cell was employed to detect time-resolved infrared absorption spectra of the reaction intermediate CH3SO2 radical, produced upon irradiation of a flowing gaseous mixture of CH3I and SO2 in CO2 at 248 nm. Two transient bands with origins at 1280 and 1076 cm(-1) were observed and are assigned to the SO2-antisymmetric and SO2-symmetric stretching modes of CH3SO2, respectively. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predicted the geometry, vibrational, and rotational parameters of CH3SO2 and CH3OSO. Based on predicted rotational parameters, the simulated absorption band of the SO2-antisymmetric stretching mode that is dominated by the b-type rotational structure agrees satisfactorily with experimental results. In addition, a band near 1159 cm(-1) observed at a later period is tentatively attributed to CH3SO2I. The reaction kinetics of CH3 + SO2 --> CH3SO2 and CH3SO2 + I --> CH3SO2I based on the rise and decay of absorption bands of CH3SO2 and CH3SO2I agree satisfactorily with previous reports.

The Vinyl + NO Reaction: Determining the Products with Time-Resolved Fourier Transform Spectroscopy

We have studied the vinyl + NO reaction using time-resolved Fourier transform emission spectroscopy, complemented by electronic structure and microcanonical RRKM rate coefficient calculations. To unambiguously determine the reaction products, three precursors are used to produce the vinyl radical by laser photolysis: vinyl bromide, methyl vinyl ketone, and vinyl iodide. The emission spectra and theoretical calculations indicate that HCN + CH2O is the only significant product channel for the C2H3 + NO reaction near room temperature, in contradiction to several reports in the literature. Although CO emission is observed when vinyl bromide is used as the precursor, it arises from the reaction of NO with photofragments other than vinyl. This conclusion is supported by the absence of CO emission when vinyl iodide or methyl vinyl ketone is used. Prompt emission from vibrationally excited NO is evidence of the competition between back dissociation and isomerization of the initially formed nitrosoethylene adduct, consistent with previous work on the pressure dependence of this reaction. Our calculations indicate that production of products is dominated by the low energy portion of the energy distribution. The calculation also predicts an upper bound of 0.19% for the branching ratio of the H2CNH + CO channel, which is consistent with our experimental results.

Molecular elimination in photolysis of fluorobenzene at 193 nm: Internal energy of HF determined with time-resolved Fourier-transform spectroscopy

Following photodissociation of fluorobenzene (C(6)H(5)F) at 193 nm, rotationally resolved emission spectra of HF(1<or= v <or= 4) in the spectral region 2800-4000 cm(-1) are detected with a step-scan Fourier-transform spectrometer. In the period 0.1-1.1 mus after photolysis, HF(v <or= 4) shows similar Boltzmann-type rotational distributions corresponding to a temperature approximately 1830 K; a short extrapolation from data in the period 0.1-4.1 mus leads to a nascent rotational temperature of 1920+/-140 K with an average rotational energy of 15+/-3 kJ mol(-1). The observed vibrational distribution of (v = 1):(v = 2):(v = 3):(v = 4) = (60+/-7):(24+/-3):(10.5+/-1.2):(5.3+/-0.5) corresponds to a vibrational temperature of 6400 +/- 180 K. An average vibrational energy of 33 +/- 9/3 kJ mol(-1) is derived based on the observed population of HF(1 <or= v <or= 4) and an estimate of the population of HF(v = 0) by extrapolation. The observed internal energy distribution of HF is consistent with that expected for the four-center (alpha,beta) elimination channel. A modified impulse model taking into account geometries and displacement vectors of transition states during bond breaking predicts satisfactorily the rotational excitation of HF. We also compare internal energies of HF observed in this work with those from photolysis of vinyl fluoride (CH(2)CHF) and 2-chloro-1,1-difluoroethene (CF(2)CHCl) at 193 nm.

The ro-vibrational spectra of CO molecule resulting from the photolysis of acetone

A time-resolved Fourier-transform emission spectroscopy was used to detect the IR emission of the fragments resulting from the photolysis of acetone by 193 nm excimer laser; a double peak vibrational spectrum in the range of 1950–2250 cm −1 corresponding to the P and R branches of the CO stretching vibration. At 0.3 cm −1 resolution; the ro-vibrational lines appeared for the first three vibrational transitions. The experimental spectra match greatly the simulated one. Using the fitting methods, the populations were found for the first four vibrational levels. The vibrational spectrum and populations of the CO resulting from the photolysis of acetone in helium differ from acetone alone due to the relaxation effect of helium.

Photolysis of oxalyl chloride (ClCO)2 at 193 nm: emission of CO(v

Upon photolysis of oxalyl chloride at 193 nm, time-resolved and rotationally resolved emission of CO(v<or=6, J<or=60) in the spectral region 1850-2350 cm(-1) was detected with a step-scan Fourier-transform spectrometer under nearly collisionless conditions. Boltzmann-type rotational distributions of CO correspond to temperatures 3520+/-110 (v=1) to 2300+/-610 K (v=6), with an average rotational energy of 23+/-2 kJ mol(-1). The average vibrational energy of CO is estimated to be 26+/-4 kJ mol(-1) according to observed vibrational populations of v=1-6 and that of v=0 predicted with a surprisal analysis. Combining the average internal energy of CO determined in this work and average translational energies of photofragments Cl and CO determined previously by Hemmi and Suits, we propose a four-body dissociation mechanism producing one pair of translationally rapid and internally excited CO and one pair of translationally rapid Cl, each with similar energies, to account for the energy balance. Formation of translationally slow ClCO, Cl, and CO reported previously by Hemmi and Suits might be rationalized with a second channel involving emission of electronically excited intermediates. We observed no emission of ClCO near 1880 cm(-1), indicating that surviving ClCO has little vibrational excitation in the C-O stretching mode.