Infrared Diode Laser Spectroscopy Research Articles

High Resolution Infrared Diode Laser Spectroscopy of C2F6in a Supersonic Jet

High resolution infrared spectra of the ν5and ν10bands of C2F6in a supersonic jet have been measured using a diode laser spectrometer. The well resolved vibration–rotation lines of these two bands were obtained. The spectra were analyzed using a standard Hamiltonian for a prolate symmetric rotor, and the precise band centers and molecular constants of this molecule have been determined.

Using diode laser spectroscopy to evaluate techniques for acceleration of etch chamber evacuation

Acceleration of vacuum chamber pumpdown through the use of species which react with adsorbed moisture is an attractive idea which appears particularly appropriate for application to a plasma-etching chamber after wet cleaning. Infrared diode laser spectroscopy was used to evaluate this technique by measuring time-dependent moisture concentrations in a metal etch chamber during evacuation and while introducing gaseous drying agents. The main advantage of this approach is that moisture levels can be measured truly in situ, with a fast response time, and with no interfering effects even in the presence of the drying agent. None of the techniques evaluated [treatment with boron trichloride, dichloropropane (DCP) and dimethoxypropane] gives any improvement in the time required to evacuate the chamber despite previously published results showing a reduction in evacuation time for an ultrahigh vacuum chamber following DCP treatment. This finding is attributed to the nature of the anodized aluminum surface of the chamber used in the present study.

Kinetics of the reaction F + NO + M → FNO + M studied by pulse radiolysis combined with time-resolved IR and UV spectroscopy

The title reaction was initiated by pulse radiolysis of SF 6/NO gas mixtures, and the formation of FNO was studied by time-resolved IR and UV spectroscopy. At SF 6 pressures of 10–320 mbar at 298 K, the formation of FNO was studied by infrared diode laser spectroscopy at 1857.324 cm −. Comparative studies were carried out at 250–1000 mbar SF 6 and temperatures of 298 and 341 K, where the formation of FNO was studied by monitoring the transient absorption of FNO at 310.5 nm. The observed pressure dependence is represented in terms of a fall-off curve with the following values of the limiting high- and low-pressure rate coefficients, k rec,∞ = (2.5 ± 0.8) × 10 10 M −1 s −1 and in the temperature range 200–400 K, and with the broadening factor, F cent = 0.878 at 298 K.

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.

High-resolution infrared diode laser spectroscopy of (CO2)3: Vibrationally averaged structures, resonant dipole vibrational shifts, and tests of CO2–CO2 pair potentials

High-resolution infrared spectra of (CO2)3 formed in a slit jet supersonic expansion are obtained via direct absorption of a tunable diode laser in the ν3 asymmetric stretch region of CO2. Over 100 distinct transitions are recorded in the trimer spectrum, which can be modeled as a perpendicular band of a planar symmetric top with C3h symmetry and no observable tunneling splittings. Results from the spectroscopic fit indicate that the complex is vibrationally averaged planar, with a carbon–carbon atom separation of RCC=4.0376(2) Å. An analysis of the vibrational blue shift for (CO2)3 of 2.5755(2) cm−1 via a resonant dipole–dipole interaction model yields an angular orientation for each CO2 axis of β=33.8(5)° away from a line tangent to the vertex and parallel to the opposite side of the equilateral triangle connecting the centers of mass of each CO2 monomer. Several model CO2–CO2 interaction potentials are tested against the vibrationally averaged structural parameters for (CO2)3. In particular, the potential of Murthy et al. [Mol. Phys. 50, 531 (1983)] reproduces RCC for the complex, but similar to all potentials tested, does not accurately predict the angular orientation β of the monomers within the trimer. Lastly, spectral evidence and model predictions suggest that there is an asymmetric top isomer of the trimer that is energetically comparable to the observed cyclic isomer.

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.

Time-resolved diode laser spectroscopy of the ν6 band of propargyl produced by the UV photolysis of allene

The propargyl radical (CH2C≡CH) produced by the ArF excimer laser photolysis of allene was observed by time-resolved infrared diode laser spectroscopy. More than one hundred and fifty absorption lines have been assigned to the ν6 (CH2-wagging) fundamental band of propargyl. Most of the absorption lines were observed as doublets due to the spin–rotation interaction in the 2B1 ground electronic state. The rotational and spin–rotation interaction constants derived for the ground vibrational state are, A0=9.608 47(36), B0=0.317 674(24), C0=0.307 098(24), εaa=−0.017 58(95), and εbb=−0.000 355(76) cm−1, where the figures in parentheses are 2.5 times standard deviations to be attached to the last digit. The ν6 band origin is 687.176 03(62) cm−1, consistent with the infrared spectrum observed in the argon matrix. Anomalously large vibrational changes in the A rotational constant and the ΔK centrifugal distortion constant are accounted for by the a-type Coriolis interaction between the ν6 and ν10 states, where ν10 is the CH2-rocking vibration.

Infrared diode laser spectroscopy of a high-temperature molecule GeS using spectrum processing by fourier transformation

The vibrational-rotational spectrum of GeS has been observed using a diode laser spectrometer equipped with a heatpipe high-temperature cell of a White cell type. Fringes due to optical reflections inside the high-temperature White cell were inherent in the observation of the spectra. However, they were eliminated, as were high-frequency noises, by Fourier manipulation of the observed diode laser spectrum. About 620 spectral lines for the Δv = 1 band sequences of the eight isotopomers, 74Ge 32S, 72Ge 32S, 70Ge 32S, 73Ge 32S, 76Ge 32S, 74Ge 34S, 72Ge 34S and 70Ge 34S have been assigned between 522 and 593 cm −1. These infrared data combined with 91 microwave data from the literature have been analyzed with a least-squares fit to a Dunham potential function with only 11 parameters which included three Watson type Δ correction terms. The Dunham Y ij coefficients have been derived for each of the eight isotopomers. The equilibrium vibrational frequency ω e of 74Ge 32S is 574.269 313(271) cm −1.

Characterization of silicon-carbon clusters by infrared laser spectroscopy. The v1 band of SiC 4

The v 1 fundamental vibration of linear SiC 4 has been observed by infrared diode laser spectroscopy of a supersonic cluster beam. Twenty-four rovibrational transitions were measured in the spectral region of 2094.6 to 2097.1 cm −1, the rotational temperature was 10 K. A combined least-squares fit of these transitions with previously reported microwave data yielded the following molecular constants: v 1 = 2095.45806(37) cm −1, B″ = 0.051161131(52) cm −1, and B′ = 0.0509157(96) cm −1. These results are compared to vibrational spectroscopy measurements of SiC 4 trapped in a solid Ar matrix and to ab initio calculations.

Infrared Diode Laser Study of Product Energy Distribution in the F+OCS Reaction

AbstractThe reaction F+OCS→SF+CO has been investigated by using infrared diode laser spectroscopy to probe both reaction products SF(2Π3/2,1/2) and CO. Fluorine atoms were prepared by pulsed CO2 laser photolysis of SF6 in the presence of OCS. Time‐resolved absorption spectra, including many rovibrational lines of SF in the v = 4‐3, 3‐2, 2‐1, and 1‐0 bands and those of CO in the v = 2‐1 and 1‐0 bands, were observed to derive nascent internal energy distributions of the reaction products. The vibrational and rotational energy distributions obtained were Boltzmann‐like, and no clear evidence for population inversion was found. Energy partitioning to vibrational modes of SF and CO was only 8 and 0.7% of total available energy (≈︁3500 cm−1), and that to rotational modes of SF and CO was 28% in both cases. These values were not so far from a statistical prior distribution (13, 2.8, 23, and 23%, respectively), indicating that the reaction F+OCS proceeds via an intermediate such as FSCO radical, which may descompose to SF and CO before complete energy randomization. No preference was observed for Λ‐doubling components of SF, while spin‐orbit component population 2Π1/2/2Π3/2 was 0.26, which was colder than the prior distribution (2Π1/2/2Π3/2 = 0.68).

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.

ChemInform Abstract: Gas‐Phase Kinetics of Free Radicals Studied by Pulse Radiolysis Combined with Time‐Resolved Infrared Diode Laser Spectroscopy

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Kinetics and thermochemistry of the reversible gas phase reaction HONO+NH 3⇌H 3H-HONO studied by infrared diode laser spectroscopy

The kinetics of the reversible reactions HONO+NH 3⇌H 3N-HONO (1) was studied by monitoring trans-HONO relaxation kinetics. The rate of approach towards equilibrium was studied as a function of the ammonia concentration to obtain values of the rate constants for the forward and reverse reactions as well as the equilibrium constant. At 298 K we have determined the following values for the forward rate constant and the equilibrium constant, k 1f=(2.2±0.2)×10 3 M −1 s −1 and K C=(1.5±0.2)×10 5 M −1. The equilibium constant was determined at temperatures in the range of 287–319 K, and from the observed temperature dependence expressed in terms of the van 't Hoff equation we have derived the following values of Δ H 298 0=−11.8±0.8 kcal/mol and Δ S 298 0=−26.7±1.0 cal/mol K. Theoretical investigations of the structure and thermochemistry of the H 3N-HONO hydrogen bonded complex were carried out on the electron correlation level and 6-311+G(2df, 2pd) basis set. The calculated binding energy is −10.1 kcal/mol while Δ H 298 0=−8.1 kcal/mol and Δ S 298 0=−26.70 cal/mol K.

Infrared diode laser spectroscopy of the Δυ = 2 band of NaBr using spectrum processing by Fourier transformation

The IR diode laser spectrum of the Δυ = 2 band of NaBr monomer has been observed with a heat-pipe high-temperature cell of a White cell type. Fringes due to optical reflections inside the high-temperature White cell were inherent in highly-sensitive observation of the spectrum. However, they were eliminated, as were high-frequency noises, by Fourier manipulation of the observed diode laser spectrum. The υ = 2-0 up to 6–4 vibration—rotation bands of both Na 79 Br and Na 81 Br, 199 lines in total, were assigned in the range between 550 and 600 cm −1 . These data, combined with 21 mm wave data from the literature, were analysed with a least squares fit to nine Dunham Y ij coefficients. Y 10 and Y 20 for Na 79 Br were determined to be 298.73648(66) and −1.21058(19) cm −1 , respectively.

Infrared diode laser spectroscopy of the ν3 fundamental and ν3+ν5−ν5 sequence bands of the C4 radical in a hollow cathode discharge

The infrared absorption spectrum of the linear C4 radical has been studied in an extension of the original observation of gas-phase C4 by Heath and Saykally [J. Chem. Phys. 94, 3271 (1991)]. The experiment was performed using a flowing mixture of acetylene and helium subjected to a hollow-cathode discharge, which was probed in the 1525–1570 cm−1 spectral region using a tunable diode laser spectrometer. Transitions with N-values up to 60 were measured. Their analysis yielded band origins, rotational, and centrifugal distortion parameters for the lower and upper vibrational states, and l-type doubling parameters for the degenerate bending states ν5 and ν3+ν5. In particular, the ν3 origin was determined to be 1548.6128(4) cm−1, the ground state rotational and centrifugal distortion parameters were B=4979.89(21) MHz and D=0.848(44) kHz, and the l-doubling parameters for ν5 was q5=10.98(13) MHz. This value for q5 was used to estimate the ν5 frequency of gas-phase C4 to be 160±4 cm−1. Both the l=0 and 2 components of the ν3+2ν5−2ν5 sequence band were also tentatively observed, but a detailed analysis was not yet possible. The results were completely consistent with a linear structure for the triplet ground state of C4, and showed no effects of quasilinearity such as that exhibited by C3.

High resolution diode laser and heterodyne spectroscopy with applications toward remote sensing

The recent developments of IR heterodyne and high resolution spectroscopy at the University of Cologne are presented. By using an impedance matched HEMT amplifier together with newly developed HgCdTe-mixers very low noise temperatures of 2100 K (DSB, corrected) have been achieved, which is only 50% above the quantum limit. In addition, very broad banded detection of the heterodyne signals was obtained with a 1.4 GHz, 2000 channel acousto-optical spectrometer. First results with a tuneable infrared diode laser as local oscillator have been obtained. For the interpretation of atmospheric absorption signals laboratory measurements of pressure effects are made using infrared diode laser spectroscopy with very high frequency resolution by frequency stabilization of the laser, and very low noise data acquisition by signal averaging methods.

Infrared diode laser spectroscopy of high-temperature molecules using spectrum processing by Fourier transformation

A heat-pipe high-temperature cell of the White cell type was constructed for sensitive detection of the spectra of high-temperature molecules. It has been incorporated into the optical system of a tunable diode laser spectrometer. With a 40 m optical path length abundant spectral lines of the Δν=2 vibration—rotation bands of NaBr have been observed in the wavenumber range between 560 and 600 cm −1. The technique of spectrum processing by use of Fourier transformation was applied to the source-modulated diode laser spectrum to eliminate fringes and to improve the signal-to-noise ratio.

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.