Time-resolved Infrared Diode Laser Spectroscopy Research Articles

Time-resolved infrared diode laser spectroscopy of the ν1 (C–O stretch) band of the CoCO radical

Infrared spectrum of the cobalt carbonyl radical CoCO produced by the 193 nm excimer laser photolysis of cobalt tricarbonyl nitrosyl Co(CO) 3NO was observed by time-resolved diode laser spectroscopy. More than 600 lines were identified as belonging to the ν 1 (C–O stretch) fundamental band, consisting of the Ω = 5 / 2 and 3/2 subbands, and the associated hot bands 1 1 2 , 1 0 1 2 1 1 , 1 0 1 3 1 1 , and 1 0 1 2 2 2 . The 2 Δ i electronic ground state of CoCO was experimentally confirmed. The ν 1 band origins are 1974.172582(93) cm −1 and 1973.53178(14) cm −1 for the Ω = 5 / 2 and 3/2 subbands, respectively. The rotational constant in the ground state was determined as B 0 = 4427.146 ( 50 ) MHz. The centrifugal distortion constant D 0 = 1.1243 ( 68 ) kHz was obtained for the Ω = 5 / 2 substate of the ground state. The equilibrium rotational constant B e = 4435.44 ( 14 ) MHz was derived, together with the vibration–rotation interaction constants.

Kinetics of the NCN Radical.

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Kinetics of the NCN Radical

The kinetics of the NCN + NO reaction has been studied using laser-induced fluorescence spectroscopy over the temperature range 298−573 K to measure total rate constants and time-resolved infrared diode laser spectroscopy as a probe for possible products. The reaction has a rate constant of k(NCN + NO) = (2.88 ± 0.2) × 10-13 cm3 molecule-1 s-1 at 298 K and low (∼3 Torr) total pressure. The rate constant displays both a temperature as well as a pressure dependence, indicating that adduct formation is a major product channel. Only very small amounts of other products were detected. Upper limits for the low-pressure rate constants of NCN + O2, C2H4, and NO2 were also obtained.

Time-resolved infrared diode laser spectroscopy of the ν3 band of the jet-cooled Fe(CO)2 radical produced by ultraviolet photolysis of Fe(CO)5

The infrared spectrum of the iron dicarbonyl radical Fe(CO)2 produced in a supersonic jet expansion by the excimer laser photolysis of iron pentacarbonyl Fe(CO)5 was observed by time-resolved infrared diode laser spectroscopy. About 170 transitions, each split into one or two fine structure components, were assigned to the ν3 (CO antisymmetric stretch) band of Fe(CO)2. The assignment was greatly facilitated by spectral simplification caused by rotational as well as vibrational cooling in the supersonic jet. It was observed that lines are missing at alternate J quantum numbers in each spin component, which confirmed that Fe(CO)2 is a linear molecule with D∞h symmetry and that the electronic ground state is of 3Σg− symmetry. The rotational and centrifugal distortion constants in the ground state were determined to be B0=1414.675(46) MHz and D0=0.3077(74) kHz, respectively. The spin–spin interaction constants obtained, λ0=655.3(42) GHz, is comparable with that of the FeCO radical, λ0=684.470(51) GHz. The ν3 band origin was determined to be 1928.184335 (82) cm−1. The figures in parentheses are uncertainties (1σ) in units of the last digit.

Product Branching Ratios of the HCO + NO2 Reaction

The reaction of HCO radicals with NO2 was studied at 298 K using time-resolved infrared diode laser spectroscopy to detect CO, CO2, and NO products. HCO was formed by the reaction of photolytically produced chlorine atoms with H2CO. After quantifying product yields and considering likely secondary reactions, we obtain the following product branching ratios: CO + NO + OH accounts for 63 ± 5%, and H + NO + CO2 accounts for the remaining 37 ± 5%. Upper limits of 10% are estimated for the CO + HONO and HNO + CO2 channels.

Experimental and theoretical studies of the reaction between CF 3 and NO 2 at 298 K

The title reaction has been studied by pulse radiolysis combined with time-resolved infrared diode laser spectroscopy. The kinetics of CF 3 were analysed taking into account the two competing reactions CF 3+ CF 3+M → C 2F 6+M (1) and CF 3+NO 2 → CF 2O+FNO (2a). Based on studies of the yield and kinetics of CF 3 we determined values of the absorption cross section, σ(CF 3)=(1.96±0.20)×10 −17 cm 2 molecule −1 at 1263.567 cm −1 and the bimolecular rate constant, k 1=(1.04±0.12)×10 −11 cm 3 molecule −1 s −1 with a bath gas pressure of 20 mbar at 298 K. Reaction (2a) was studied under pseudo-first-order conditions and the value of k 2a=(1.53±0.20)×10 −11 cm 3 molecule −1 s −1 was found to be independent of bath gas pressure in the range 4–22 mbar. Based on the characteristic absorption spectra of the products, the branching ratio of reaction (2a) was found to be 0.95.

Time-resolved infrared diode laser spectroscopy of jet-cooled FeCO and Fe(CO) 2 radicals produced by the UV photolysis of Fe(CO) 5

Time-resolved infrared diode laser spectroscopy was applied to the observation of jet-cooled iron carbonyl radicals, FeCO and Fe(CO) 2, produced by the ArF excimer laser photolysis of iron pentacarbonyl, Fe(CO) 5. The rotational temperature of 38±6 K was observed for FeCO. Simplification of the spectrum caused by jet cooling facilitated the assignment of the ν 3 band of Fe(CO) 2, whose band origin was determined to be 1928.18408(13) cm −1. It was confirmed by the observation of alternatively missing spin components in the ν 3 band spectrum of Fe(CO) 2 that this radical is linear and symmetric (D ∞h) and that the electronic ground state is of 3Σ g − symmetry.

Product Branching Ratios of the NH2(X2B1) + NO2 Reaction

The reaction of NH2(X2B1) with NO2 was studied at 298 K using time-resolved infrared diode laser spectroscopy to detect N2O and NO products. The N2O + H2O channel was confirmed to be a rather minor contribution to the overall reaction, with a branching ratio of 0.24 ± 0.04. The branching ratio of the NO + H2NO channel was measured to be 0.76 ± 0.1.

Time-resolved infrared diode laser spectroscopy of the ν1 band of the iron carbonyl radical (FeCO) produced by the ultraviolet photolysis of Fe(CO)5

The infrared spectrum of the iron carbonyl radical FeCO generated by the 193 nm excimer laser photolysis of iron pentacarbonyl Fe(CO)5 was observed by time-resolved diode laser spectroscopy. The 85 lines, mostly observed as triplets split by the electron spin-spin interaction, were assigned to the ν1 (CO stretch) band of FeCO. The electronic ground state of FeCO was confirmed experimentally to have 3Σ− symmetry. Molecular constants in the ground and ν1 vibrational states were derived from an analysis of the infrared spectrum combined with pure rotational lines in the lowest spin component Ω=0 observed by Fourier transform microwave (FTMW) spectroscopy. The rotational and centrifugal distortion constants in the ground state were determined as B0=4364.266(55) MHz and D0=1.378(25) kHz, where the figures in parentheses are standard errors to be attached to the last digit. The spin-spin and spin-rotation coupling constants are λ0=663.1(40) GHz and γ0=−974(27) MHz, respectively. The origin of the ν1 vibrational band determined is 1946.470 60(12) cm−1, which is consistent with the value derived from photodetachment spectroscopy of the FeCO− anion. The collisional quenching rate of FeCO by Fe(CO)5 was measured to be 1.13(4)×10−10 cm3 molec −1 s−1 by a kinetic study.

Kinetics and branching ratios of the reactions NH 2 + NO 2 → N 2O + H 2O and NH 2 + NO 2 → H 2NO + NO studied by pulse radiolysis combined with time-resolved infrared diode laser spectroscopy

The source reaction F + NH 3 → HF + NH 2 was initiated by the pulse radiolysis of NH 3/SF 6 mixtures, and the primary yield of F atoms was determined by monitoring the decrease in the infrared absorption of methane consumed in the titration reaction F + CH 4 → HF + CH 3. The title reactions have been studied by monitoring the decay of NH 2 and the simultaneous formation of N 2O and NO by time-resolved infrared diode laser spectroscopy. The decay rate of NH 2 was studied as a function of NO 2 concentration to obtain an overall rate constant k(NH 2 + NO 2) = (1.35 ± 0.15) × 10 −11 molecule −1 cm 3 s −1 at 298 K and with a bath gas pressure of p(SF 6) = 40 mbar. Two product channels have been identified, N 2O + H 2O and H 2NO + NO, with relative yields of (59 ± 3)% and (40 ± 5)%, respectively.

Time-resolved infrared diode laser spectroscopy of the ν5 band of the cyanomethyl radical (H2CCN)

The infrared spectrum of the cyanomethyl radical (H2CCN) generated by the 193 nm excimer laser photolysis of chloroacetonitrile was observed by time-resolved diode laser spectroscopy. About 50 lines, involving those split into doublet due to the spin–rotation interaction, were assigned to rovibrational transitions in the ν5 (CH2-wagging) band of cyanomethyl. The molecular constants in the ν5 vibrational state were derived from the analysis of the observed wave numbers, resulting in the rotational constants, A=9.095 03(21) cm−1, (B+C)/2=0.335 363 4(41) cm−1, and (B−C)=0.011 503 6(71) cm−1, and the spin–rotation interaction constant εaa=−2.143(47)×10−2 cm−1, where the figures in parentheses are 2.5 standard deviations to be attached to the last digit, the constants in the ground state being fixed to the reported values from microwave spectroscopy. The band origin determined ν0=663.793 98(85) cm−1 is consistent with the value derived from the photo-detachment spectroscopy of the H2CCN− anion. Large changes in the rotational constant A and the centrifugal distortion constant ΔK on vibrational excitation from the ground state to the ν5 state are accounted for by the a-type Coriolis interaction of the ν5 vibrational state with the ν8 (CH2-rocking) and ν9 (in-plane ∠CCN-bending) vibrational states.

Diode Laser Study of the Product Branching Ratio of the NH2(X 2B1) + NO2 Reaction

The reaction of NH{sub 2}(X {sup 2}B{sub 1}) with NO{sub 2} was studied at room temperature using time-resolved infrared diode laser spectroscopy to detect N{sub 2}O, H{sub 2}O, and NO products. The N{sub 2}O + H{sub 2}O product channel was found to have a branching ratio of 0.14{+-}0.02. Large amounts of NO were detected, but secondary sources of this species prevent a quantitative determination of the branching ratio into the H{sub 2}NO + NO channel. These results are in contrast to previously published branching ratio data. 42 refs., 4 figs., 1 tab.

Product Branching Ratios of the NH (3.SIGMA.-) + NO and NH (3.SIGMA.-) + NO2 Reactions

The title reactions were studied at 298 K using time-resolved infrared diode laser spectroscopy. For the NH ({sup 3}{Sigma}{sup -}) + NO reaction, N{sub 2}O + H were found to be the primary products, with a branching ratio of 0.77 {+-} 0.08, in good agreement with other recent measurements. For the NH ({sup 3} {Sigma}{sup -}) + NO{sub 2} reaction, the measured branching ratio was 0.41 {+-} 0.15 into the N{sub 2}O + OH channel and 0.59 {+-} 0.15 into the NO + HNO channel. 45 refs., 5 figs., 3 tabs.

Formation of SiF 2 in the infrared multiphoton decomposition of Si 2F 6 and the reactions of SiF 2 with Br 2, NO 2 and C 2H 4

The infrared multiphoton decomposition of Si 2F 6 has been investigated by time-resolved infrared diode laser spectroscopy. Direct formation of SiF 2 (X̃ 1A 1) in the ground vibrational state and indirect formation via vibrational relaxation were found. Simultaneous formation of SiF 4 with SiF 2 was also observed, indicating that a 1,2-fluorine shift occures in preference to SiSi bond scission. The vibrational relaxation of SiF 2 in H 2 was found to be about twenty times faster than that in N 2 because of resonant vibration-rotation energy transfer. The rate constants for the reactions of SiF 2 with Br 2, NO 2 and C 2H 4 were determined as (7.6 ± 1.0) × 10 −13, (5.8 ± 0.9) × 10 −13 and < 1 × 10 −15 cm 3 molecule −1s −1, respectively, at room temperature.

Infrared diode laser spectroscopic detection of the propargyl radical produced in a supersonic jet expansion by UV laser photolysis

The propargyl radical (CH 2CCH) was produced in a pulsed supersonic jet expansion by the 193 nm excimer laser photolysis of propargyl chloride, and detected by the method of time-resolved infrared diode laser spectroscopy. A rotational temperature of 16 ± 4 K was obtained in an experiment in which the τQ 0-branch lines of the v 6 band were observed. The characteristic behavior of the propargyl radical in a supersonic beam produced by circular and slit nozzles was discussed.

The H+OCS hot atom reaction: CO state distributions and translational energy from time-resolved infrared absorption spectroscopy

Time-resolved infrared diode laser spectroscopy has been used to probe CO internal and translational excitation from the reaction of hot H atoms with OCS. Product distributions should be strongly biased toward the maximum 1.4 eV collision energy obtained from 278 nm pulsed photolysis of HI. Rotations and vibrations are both colder than predicted by statistical density of states theory, as evidenced by large positive surprisal parameters. The bias against rotation is stronger than that against vibration, with measurable population as high as v=4. The average CO internal excitation is 1920 cm−1, accounting for only 13% of the available energy. Of the energy balance, time-resolved sub-Doppler line shape measurements show that more than 38% appears as relative translation of the separating CO and SH fragments. Studies of the relaxation kinetics indicate that some rotational energy transfer occurs on the time scale of our measurements, but the distributions do not relax sufficiently to alter our conclusions. Vibrational distributions are nascent, though vibrational relaxation of excited CO is unusually fast in the OCS bath, with rates approaching 3% of gas kinetic for v=1. At 9720 cm−1 above the activation barrier, energy partitioning is consistent with incomplete IVR in an HSCO intermediate, followed by repulsive release of a large fraction of the available energy into relative translation.

CO internal excitation in the photodissociation of Cr(CO)6 at 278 nm

Time-resolved infrared diode laser spectroscopy has been used to probe CO internal excitation in the photodissociation of Cr(CO)6 at 278 nm. At the high fluence level of these experiments, CO state distributions are not consistent with a statistical model of single-photon absorption. A simple Franck—Condon treatment, assuming multiphoton absorption into a dissociative continuum, qualitatively describes the observed CO vibrational distribution.

Rate constant measurements for reactions of SiH3 with O2, NO and NO2 using time-resolved infrared diode laser spectroscopy

The rate constants for the reactions SiH3+O2, SiH3+NO2 and SiH3+NO+N2 have been measured over the pressure range 1–10 Torr at 300 K, by monitoring a SiH3 absorption line at 719.931 cm−1 using time-resolved diode laser spectroscopy. SiH3 radicals were prepared by pulsed CO2 laser photolysis of CCl3F in SiH4: CCl3F + nhv → CCl2F + Cl, Cl + SiH4 → HCl + SiH3. Analysis of the pseudo-first-order decay of SiH3 provided rate constants of (1.3 ± 0.3) × 10−11 and (5.1 ± 0.9) × 10−11 cm3 molecule−1 s−1 (±2σ) for the reactions with O2 and NO2 respectively and 8.2 ± 0.9 × 10−30 cm6 molecule−2 s−1 (±2σ) for the reaction SiH3 + NO + N2.