Laser Magnetic Resonance Spectrometer Research Articles

Discovery and characterization of optically pumped far-infrared laser emissions using laser magnetic resonance spectroscopy

A laser magnetic resonance spectrometer has been used to discover and subsequently measure a far-infrared laser emission: the 166.6-micron line of CH2F2, optically pumped by the 9P24 CO2 laser. By recording spectra for the NH radical, the frequency of this laser emission has been determined to be 1799950±13 MHz. Spectra for the NH radical were also recorded with two other far-infrared laser emissions: the 160.4-micron line of N2H4 (9P46 CO2 pump) and the 328.6-micron line of 13CH3OH (9P12 CO2 pump). From the NH spectra, a discrepancy of 2.1 GHz with the previously measured laser frequency was identified for the 160.4-micron line. A three-laser heterodyne system was then used to remeasure the frequency to be 1868475.5±0.5 MHz. The NH spectra were also used to determine the frequency for the 328.6-micron line to be 912366±7 MHz, in agreement with the value previously calculated from the Rydberg–Ritz combination principle.

Studies of the mid- and far-infrared laser magnetic resonance spectra of the CD radical: information on vibrationally excited levels

Two separate studies of the CD radical in vibrationally excited levels of its X 2 Π ground state have been made by the technique of laser magnetic resonance. The first of these studies was in the far-infrared; rotational transitions of CD in the v = 1 and 2 levels have been detected. The second study was carried out in the mid-infrared using a carbon monoxide laser magnetic resonance spectrometer. In these experiments, transitions in the (1,0), (2,1), and (3,2) bands have been detected. All the available data on CD in its X 2 Π state have been used to determine an improved set of molecular parameters for the CD radical. In addition to the above data sets, previous far-infrared laser magnetic resonance on the CD radical in the v = 0 level and FTIR observations of the (1,0) and (2,1) bands have been included. The principal molecular parameters determined are: ν 0 = 2032.03360 ( 18 ) cm - 1 , ω e x e = 34.72785 ( 58 ) cm - 1 , B 0 = 7.7018632 ( 14 ) cm - 1 , α B = - α e = - 0.212239 ( 11 ) cm - 1 , where the figures given in parentheses are one standard deviation from the least squares fit. A small but significant dependence of the orbital contribution to the magnetic dipole moment on the vibrational quantum number is detected. This may reflect the mixing between the X 2 Π and a 4 Σ - states of CD.

Measurement of the electric dipole moment of NO (X2 Π ν = 0,1) by mid-infrared laser magnetic resonance spectroscopy

A pair of parallel Stark plates are added to a CO laser magnetic resonance spectrometer to apply electric field in the absorption cell. This apparatus is used to measure the molecular electric dipole moment via Zeeman and Stark effects simultaneously. The saturated absorption spectra of NO (X2Π3/2, ν = 1 ← 0) was observed and the electric dipole moments of NO were directly measured in the presence of an electric field. The dipole moments are determined as μ0(ν = 0) = 0.1595(15) D, μ1 (ν = 1) = 0.1425(16) D. The electric dipole moment of the vibrationally excited state (ν = 1) is determined for the first time. The dependence of the electric dipole moments on its nuclear distances is interpreted.

Application of Laser Magnetic Resonance Spectroscopy to theMeasurement of Electric Dipole Moment of Free Radicals

An intracavity CO laser magnetic resonancespectrometer with homogeneous dc electric field applied via a pair ofparallel Stark plates in the absorption cell is used to measure theelectric dipole moments of free radicals. Taking advantage of the highsensitivity and high resolution of this technique and the Stark effect,highly-resolved saturated absorption spectra of the ν = 1-0 transition of15N16O in the ground state X2Π3/2 have beensuccessfully observed in the presence of a low electric field. Theelectric dipole moment of NO in the electronic ground state is determinedas µ = 0.1566±14 D (Debye) from the analysis of the observedspectra, confirming that, combined with the Stark field, the lasermagnetic resonance technique can be an effective and reliable approach forthe precise measurement of electric dipole moments of free radicals,especially unstable ones.

Measurement of the pressure-broadening coefficient of NO by saturation spectroscopy of LMR

This paper presents a method for the determination of the pressure-broadening coefficient of 15N16O by 14N16O. The hyperfine-structure-resolved spectral lines of NO were obtained with an intracavity laser magnetic resonance spectrometer via Lamb dips. From the spectra, the self-broadening coefficient of the P2(5/2) transition of the 15N16O fundamental band due to its collision with 14N16O at 293 K is determined to be 0.092(7) cm–1/atm. PACS No.: 32.40

Rotational Spectrum of the AsH2 Radical in Its Ground State, Studied by Far-Infrared Laser Magnetic Resonance

The rotational spectrum of AsH2 in its ground X̃2B1 electronic state has been recorded using a far-infrared laser magnetic resonance spectrometer. The AsH2 radical was produced inside the spectrometer cavity by the reaction of arsine (AsH3) with fluorine atoms. Hyperfine splittings from both 75As and 1H nuclei were observed, and analysis of the spectra has yielded accurate values for rotational, hyperfine, and Zeeman parameters.

Measurement of the pressure-broadening coefficient of NO by saturation spectroscopy of LMR

This paper presents a method for the determination of the pressure-broadening coefficient of 15N16O by 14N16O. The hyperfine-structure-resolved spectral lines of NO were obtained with an intracavity laser magnetic resonance spectrometer via Lamb dips. From the spectra, the self-broadening coefficient of the P2(5/2) transition of the 15N16O fundamental band due to its collision with 14N16O at 293 K is determined to be 0.092(7) cm–1/atm. PACS No.: 32.40

A far-infrared laser magnetic resonance spectrometer for the investigation of radicals of atmospheric relevance

A far-infrared laser magnetic resonance spectrometer is described. A superconducting magnet is used for the tuning of the energy levels. Pressure broadening measurements of OH and NO have been performed. The measurements demonstrate that the laser magnetic resonance technique is well suited for this kind of measurements. Based on this results the design and expected performance of a compact laser magnetic resonance spectrometer is presented. The sensitivity as well as the mechanical ruggedness of this spectrometer is sufficient in order to be used aboard an aircraft for the in situ detection of OH and HO 2 in the lower stratosphere and upper troposphere.

CO LASER MAGNETIC RESONANCE SPECTRUM OF 15N16O AND ITS ANALYSIS WITH SPECTRA OF 15N17O AND 15N18O

Employing the intracavity absorption technique,Lamb dip of the spectrum was obtained and the resolution and sensitivity of CO Laser magnetic resonance(LMR) spectrometer was greatly improved. By this technique, the X2Π3/2(υ=1←0) Zeeman transitions of 15N16O were observed with the Λ-doubling and hyperfine structures resolved. A correlative analysis of the LMR Spectrum of 15N16O with the previous available measurements was performed. The global least-square fit provided by far the most complete and the most accurate molecular constants of all the related isotopic species of 15NmO(m=16—18). The accuracy of these constants is improved by 1 or 2 orders. Many of the molecular constants including γ, AD, Δ01, Δ10, Δ00 were determined for the first time.

A far-infrared laser magnetic resonance spectrometer with permanent magnets

A laser magnetic resonance spectrometer for the far-infrared region is described. It is based on an optically pumped far-infrared laser. Zeeman tuning of the energy levels of the investigated molecule is achieved by using permanent magnets. With this setup it is possible to reach a magnetic flux density as high as 0.5 T. The design of the spectrometer is very compact compared to conventional laser magnetic resonance spectrometers based on superconducting or watercooled electromagnets. This makes it a promising tool for analytic purposes either in the laboratory or for field studies.

Rotational Spectrum of the AsH Radical in Itsa1Δ State, Studied by Far-Infrared Laser Magnetic Resonance

The rotational spectrum of AsH in its metastablea1Δ state has been recorded using a far-infrared laser magnetic resonance spectrometer. The AsH radical was produced inside the spectrometer by the reaction of arsine (AsH3) with fluorine atoms. Hyperfine splittings from both75As and1H nuclei were observed, and analysis of the spectra yielded accurate values for rotational, hyperfine, and Zeeman parameters.

Primary products of the elementary reactions of CH2CO with F, Cl, and OH in the gas phase

AbstractThe absolute yields of the primary products of the reactions of CH2OH with F and Cl atoms and OH radicals were measured in the gas phase at room temperature using a discharge flow apparatus connected to a Far Infrared Laser Magnetic Resonance (FIR‐LMR) spectrometer. Quantitative determinations of the reaction pathways were carried out by employing reference reactions with known product yields. The measurements yielded the branching ratios for the following channelsmagnified imageThus, the main reaction channels were found to be addition of the F, Cl, or OH, respectively, to the CH2 moiety followed by elimination of CO.

The Infrared Spectrum of Isotopomers of the TeH Radical, Observed by CO Laser Magnetic Resonance

The infrared spectrum of the TeH radical in its X 2Π state has been recorded using an intracavity CO laser magnetic resonance (LMR) spectrometer. Seven of the eight naturally occurring Te isotopomers were observed, with resonances originating from the first three vibrational levels; many were recorded as Lamb-dips. These observations have been combined with existing data for TeH and TeD in the X 2Π state and used to determine the parameters of an N 2 Hamiltonian, including isotopic scaling and nonadiabatic corrections. The data are well described by the parameters. The different isotopic dependences of the effects of the parameters A D and γ has allowed their separation and the extent to which TeH shows Hund′s case (c) coupling is discussed. Trends displayed by the chalcogen monohydrides are considered.

Submillimeter EPR evidence for the As antisite defect in GaAs

A new EPR spectrum has been observed in semi-insulating GaAs with a sub- millimeter laser magnetic resonance spectrometer. The spectrum is isotropic with g = 2.04 ± 0.01 at ʋ ̃ = 11.236 cm −1 . The hyperfine interaction parameter |A | ( I = 3 2 ) is 0.090 ± 0.001 cm -1.The spectrum is attributed to the As antisite defect in GaAs and the parameters are compatible with the P antisite defect in GaP.

Kinetics of the Reaction of OH Radicals with CH2CO

AbstractThe kinetics of the homogeneous gas phase reaction OH + CH2CO → products (1) has been investigated at room temperature and pressures between 1.4 mbar ≤ p ≤ 2.5 mbar using the discharge flow method. Reactors with Teflon wall coatings and with different surface‐to‐volume ratios were employed to exclude effects of heterogeneous reactions. OH radicals were generated via the reaction F + H2O. Their concentration‐versus‐time decay profiles were followed under pseudo‐first‐order conditions, [CH2CO] → [OH]0 with a Far Infrared Laser Magnetic Resonance (FIR‐LMR) spectrometer. The rate constant of the title reaction was found to be k1, (296 K) = (7.2 ± 2.0)·1012 cm3/mol·s.

Kinetics of the reactions of methylene (X3B1)-radicals with nitric oxide and nitrogen dioxide

The kinetics of the reactions of CH{sub 2} radicals in their triplet electronic ground state ({tilde X}{sup 3}B{sub 1}) with NO and NO{sub 2} (CH{sub 2}({tilde X}{sup 3}B{sub 1}) + NO {yields} products (1); CH{sub 2}({tilde X}{sup 3}B{sub 1}) + NO{sub 2} {yields} products (2)) have been studied at room temperature in isothermal discharge flow systems. CH{sub 2} radicals were generated either by exciplex laser photolysis of CH{sub 2}CO or via the reaction O + CH{sub 2}CO {yields} CH{sub 2} + CO{sub 2}. The CH{sub 2} concentration was monitored directly with a far-infrared laser magnetic resonance spectrometer. From the decay of (CH{sub 2}) under pseudo-first-order conditions the rate constants of reactions 1 and 2 were obtained to be k{sub 1}(296K) = (2.2 {plus minus} 0.5) {times} 10{sup 13} cm{sup 3}/(mol s) and k{sub 2}(296K) = (5.9 {plus minus} 1.4) {times} 10{sup 13} cm{sup 3}/(mol s).

ChemInform Abstract: Kinetic Studies of the Reactions of HSO with NO2, NO, and O2.

A far-infrared rotational transition in HSO has been observed by using an optically pumped laser magnetic resonance (LMR) spectrometer. LMR detection of HSO was utilized to study the reactions of HSO with NO/sub 2/, NO, and O/sub 2/. Rate coefficients were measured under pseudo-first-order conditions in a discharge flow system coupled to the spectrometer. The results are k(HSO + NO/sub 2/) = (9.6 +/- 2.4) x 10/sup -12/ cm/sup 3/ molecule/sup -1/ s/sup -1/; k(HSO + NO) less than or equal to 1 x 10/sup -15/ cm/sup 3/ molecule/sup -1/ s/sup -1/; and k(HSO + O/sub 2/) less than or equal to 2 x 10/sup -17/ cm/sup 3/ molecule/sup -1/ s/sup -1/. All measurements were made at low pressure (1-5 Torr) and room temperature (296 +/- 3 K). Experiments were also conducted to determine the products of the HSO + NO/sub 2/ reaction. The results show that a species is produced which reacts with O/sub 2/ to form HO/sub 2/ with a rate coefficient of (3 +/- 2) x 10/sup -13/ cm/sup 3/ molecule/sup -1/ s/sup -1/ which was determined from the rate of HO/sub 2/ formation. They propose that the unidentified intermediate is HSO/sub 2/.

Kinetics of the reactions of CH 2 ( 3B 1-radicals with C 2H 2 and C 4H 2 in the temperature range 296 K≤T≤700 K

The reactions of CH2-radical in the triplet electronic ground state3B1 (3CH2) with acetylene and diacetylene C3H2+C2H2→products(1)C3H2+C4H2→products(2) were studied in the gas phase in isothermal discharge flow reactors. CH2-radicals were generated in two different sources using the reaction O + CH2CO or exciplex laser photolysis of CH2CO. The 3CH2 depletion was monitored under pseudo-first-order conditions with C2H2 or C4H2 being present in great excess with a far infrared Laser Magnetic Resonance (LMR) spectrometer. In the temperature range 296 K≤T≤700 K the following rate constants were measured: k1exp⁡=(3.0±1.6)⋅1013exp⁡(−(30.7±1.7)kJmol−1/RT)cm3/molsk2exp⁡=(1.5±0.9)⋅1013exp⁡(−(18.4±1.6)kJmol−1/RT)cm3/mols. Correcting for small contributions to the depletion of 3CH2 due to collisional excitation of 3CH2 to the singlet first excited state ã 1A1 (1CH2), the rate constants for the direct reactions of 3CH2 with C2H2 and C4H2 were obtained to be k1=(1.2±0.5)⋅1013exp⁡(−(27.7±1.4)kJmol−1/RT)cm3/molsk=(1.3±0.8)⋅1013exp⁡(−(18.0±1.5)kJmol−1/RT)cm3/mols.

Kinetic studies of the reactions of mercaptooxy with nitrogen dioxide, nitric oxide, and oxygen

A far-infrared rotational transition in HSO has been observed by using an optically pumped laser magnetic resonance (LMR) spectrometer. LMR detection of HSO was utilized to study the reactions of HSO with NO/sub 2/, NO, and O/sub 2/. Rate coefficients were measured under pseudo-first-order conditions in a discharge flow system coupled to the spectrometer. The results are k(HSO + NO/sub 2/) = (9.6 +/- 2.4) x 10/sup -12/ cm/sup 3/ molecule/sup -1/ s/sup -1/; k(HSO + NO) less than or equal to 1 x 10/sup -15/ cm/sup 3/ molecule/sup -1/ s/sup -1/; and k(HSO + O/sub 2/) less than or equal to 2 x 10/sup -17/ cm/sup 3/ molecule/sup -1/ s/sup -1/. All measurements were made at low pressure (1-5 Torr) and room temperature (296 +/- 3 K). Experiments were also conducted to determine the products of the HSO + NO/sub 2/ reaction. The results show that a species is produced which reacts with O/sub 2/ to form HO/sub 2/ with a rate coefficient of (3 +/- 2) x 10/sup -13/ cm/sup 3/ molecule/sup -1/ s/sup -1/ which was determined from the rate of HO/sub 2/ formation. They propose that the unidentified intermediate is HSO/sub 2/.

A direct study of the reactions of methylene(~X 3B1) radicals with hydrogen and deuterium atoms

The following reactions of CH/sub 2/ radicals in their triplet electronic ground state X(tilde) /sup 3/B/sub 1/ with hydrogen and deuterium atoms were investigated at room temperature and pressures of a few mbar in an isothermal discharge flow reactor: CH/sub 2/(X(tilde) /sup 3/B/sub 1/) + H(/sup 2/S) ..-->.. CH(/sup 2/II) + H/sup 2/(/sup 1/..sigma..) (1a) ..-->.. CH/sub 3/(/sup 2/A/sub 2/'') (1b); CH/sub 2/(X(tilde) /sup 3/B/sub 1/) + D(/sup 2/S) ..-->.. CH(/sup 2/II) + HD(/sup 1/..sigma..) (2a), ..-->.. CD(/sup 2/II) + H/sub 2/(/sup 1/..sigma..) (2b), ..-->.. CHD(/sup 3/B/sub 1/) + H(/sup 2/S) (2c), ..-->.. CH/sub 2/D(/sup 2/A/sub 2/'') (2d). CH/sub 2/ and CH radicals were detected with a far-infrared laser magnetic resonance (LMR) spectrometer while H and D atoms were monitored via their Lyman-..cap alpha.. vacuum ultraviolet resonance absorption. Direct measurements of the pseudo-first-order decay of (CH/sub 2/) in the presence of an excess of H or D yielded the rate constants k/sub 1/(298 K) = (1.1 +/- 0.3) x 10/sup 14/ cm/sup 3//(mol s) and k/sub 2/(298 K) = (1.1 +/- 0.3) x 10/sup 14/ cm/sup 3//(mol s). Under the conditions used the recombination channels 1b and 2d are negligible. Thus, the measured values correspond to k/sub 1/ = k/submore » 1a/ and k/sub 2/ = K/sub 2a/ = k/sub 2b/ = k/sub 2c/. When the value for k/sub 1a/ is combined with literature data for the reverse reaction CH + H/sub 2/ ..-->.. CH/sub 2/ + H (-1a), the heat of formation of CH/sub 2/ radicals was found to be ..delta..H/sub f//sup 0/ /sub 298/(CH/sub 2/(X(tilde)/sup 3/B/sub 1/)) = 389 +/- 4 kJ/mol.« less