Far-infrared Laser Magnetic Resonance Research Articles

The rotational spectrum of the FeD radical in its X Δ4 state, measured by far-infrared laser magnetic resonance

Transitions between the spin-rotational levels of the FeD radical in the v=0 level of the X (4)Delta ground state have been detected by the technique of laser magnetic resonance at far-infrared wavelengths. Pure-rotational transitions have been observed for the three lowest spin components. Lambda-type doubling is resolved on all the observed transitions; nuclear hyperfine structure is not observed. The energy levels of FeD are strongly affected by the breakdown of the Born-Oppenheimer approximation and cannot be modeled accurately by an effective Hamiltonian. The data are therefore fitted to an empirical formula to yield term values and g-factors for the various spin-rotational levels involved.

Spectroscopic study of the 14NH radical in vibrationally excited levels of the X3Σ− state by far infrared laser magnetic resonance

Rotational transitions of vibrationally excited NH (ν = 1 and 2) in the ground X3Σ− electronic state have been detected by far-infrared laser magnetic resonance. The first four rotational intervals were investigated (N = 1 − 0, 2 − 1, 3 − 2, and 4 − 3) with a total of 17 far-infrared laser lines ranging in wavelength from 81.1 to 373.6 µm. For some rotational intervals, transitions between all components of the Zeeman manifolds were observed. An effective Hamiltonian was used to model the experimental measurements. The magnetic hyperfine parameters have been determined for the first time for the ν = 2 level and have been significantly improved for the ν = 1 level. In addition, the rotational, centrifugal distortion, spin-spin, spin-rotation, and Zeeman parameters have all been experimentally determined for the ν = 1 and 2 levels of NH.

The rotational and fine-structure spectrum of FeH, studied by far-infrared laser magnetic resonance

Transitions between the spin-rotational levels of the FeH radical in the upsilon=0 level of the X (4)Delta ground state have been detected by the technique of laser magnetic resonance at far-infrared wavelengths. Both pure rotational and fine-structure transitions have been observed; lambda-type doubling is resolved on all the observed transitions. The energy levels of FeH are strongly affected by the breakdown of the Born-Oppenheimer approximation and cannot be modeled accurately by an effective Hamiltonian. The data are therefore fitted to an empirical formula to yield term values and g factors for the various spin-rotational levels involved. Many of the resonances show a doubling that arises from the proton hyperfine structure. These splittings are analyzed in a similar manner.

Assignment of far-infrared laser magnetic resonance spectrum of CH 2Br radical at 447.3 and 672.1 μm

Assignment of far-infrared laser magnetic resonance spectrum of CH 2Br radical at 447.3 and 672.1 μm

Part of the far-infrared laser magnetic resonance spectrum of the HF + free radical

Transitions between the spin-rotational levels of the HF + radical in the v=0 level of the X 2Π ground state have been observed by the technique of laser magnetic resonance at far-infrared wavelengths. Because of the large spin–orbit coupling in this 2Π state, the detection of the fine-structure transitions required the use of very short-wavelength laser lines (down to 40 μm). These observations have provided accurate information on the 19F hyperfine splittings in rotational levels of the upper 2 Π 1/2 spin component for the first time which has enabled the complete determination of the hyperfine structure for this molecule. An effective Hamiltonian was used to model the experimental measurements; this provided considerably more accurate values for the various molecular parameters than previously available. Using these parameters, predictions of the transition frequencies between the low-lying spin-rotational levels of the radical at zero magnetic field have been made.

The far-infrared laser magnetic resonance spectrum of the 13CH radical

Transitions between the spin-rotational levels of the 13CH radical in the v=0 level of the X 2 Π ground state have been detected by the technique of laser magnetic resonance at far-infrared wavelengths. These measurements have been combined with the previous measurements of the lambda-doubling intervals of the molecule [J. Chem. Phys. 85 (1986) 1276 ] to determine an improved set of molecular parameters for 13CH. The analysis provides accurate predictions of the transition frequencies between the low-lying spin-rotational levels of the radical at zero magnetic field. A comparison is made with the values of the corresponding parameters of 12CH which reveals small effects due to the breakdown of the Born–Oppenheimer approximation.

Far-infrared detection of $^{\mathsf{17}}$OH towards Sagittarius B2

The frequencies and line strengths of the 2 Π3/2 J = 5/2-3/2 rotational transition of 17 OH have been calculated from an analysis of its far-infrared laser magnetic resonance spectrum. These results have been used to make the first detection of a pure rotational transition of 17 OH in the ISM. Two resolved components of this transition appear in absorption towards the giant molecular cloud Sagittarius B2, which was observed at a spectral resolution of 33 km s −1 with the Fabry-Perot mode of the ISO Long Wavelength Spectrometer. The corresponding transition of 18 OH was also observed and its line shape was modelled using H  measurements. The 18 O/ 17 O ratio of 3.5 was then used to compare this with the observed 17 OH line shape.

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.

Analysis of far-infrared laser magnetic resonance spectra of CH 2 Br at 447.3 and 671.1µm

A simple model has been developed to describe the Zeeman patterns of far-infrared laser magnetic resonance spectra of the monobromomethyl radical CH2Br observed at 447.3 and 671.1mum. A satisfactory agreement between the experimental spectra of the radical and their simulation with this simple model has been achieved. This approach can be used to gain further information about the structure and the spectrum of this interesting radical.

High-Resolution Spectroscopic Measurements of the ν5 Bending Vibration–Rotation Band of HCCN in its X̃3Σ− State at 129 cm−1

The HCCN radical is known to be a quasi-linear molecule in its ground triplet state (3Σ− in the linear configuration). Vibration–rotation transitions in the HCC bending (ν5) fundamental band have been detected around 129 cm−1 by the technique of far-infrared laser magnetic resonance (FIR LMR). Four FIR laser lines were used to record a total of 530 resonances. The observed transitions can be regarded equivalently as Ka=1←0 transitions of a bent molecule or as l5=1←0 transitions of a linear molecule. The LMR data, combined with previous measurements on this molecule at microwave and submillimeter wavelengths, have been used to determine parameters of an asymmetric rotor Hamiltonian. The ν5 band origin has been determined more accurately as 128.907 968 7 (40) cm−1. In addition, it has been possible to characterize the electron spin splittings in the Ka=1 levels more reliably. Both 1H and 14N hyperfine splittings have been observed for the Ka=1 levels for the first time; they show that the nuclear spin–electron spin dipolar interactions are markedly noncylindrical. Values for the electron spin and rotational g-factors (gααs and gααr) have also been determined.

Far-infrared LMR spectroscopic investigation of the quasi-linear molecule DCCN: The v5(1 0) transition

The far-infrared laser magnetic resonance spectrum (FIR LMR) of the v5 bending vibrational transition of DCCN in its X3 Σ– state is reported. The DCCN radical was produced inside the spectrometer cavity by the reaction of deuterated acetonitrile with F atoms. DCCN resonances were measured on seven laser lines. Nitrogen hyperfine structure was observed on a number of the resonances. The analysis provides improved accuracy for the separation v5= 1 [Formula: see text] 0 and some of the 14N hyperfine coupling constants for this isotopomer.PACS No.: 33.20Ea

Far-Infrared Laser Magnetic Resonance Spectroscopic Study of the ν2 Bending Fundamental of the CCN Radical in Its X̃2Πr State

Bending vibration–rotation transitions between the (010) μ2Σ− and (000) 2Πr vibronic states of the CCN radical in its ground electronic state have been observed using far-infrared laser magnetic resonance (FIR LMR) spectroscopy. Thirteen FIR laser lines were used to record 769 resonances. The LMR data, combined with previous data, were used to determine vibrational, Renner–Teller, fine-structure, rotational, hyperfine, and molecular g-factor parameters using a least-squares fitting routine. The model used was an N2 effective Hamiltonian modified to include the Renner–Teller effect explicitly in a 2Π electronic state. The band origin for the (010) μ2Σ− ← (000) X̃2Πr transition was determined to be 179.598176 ± 0.000067 cm−1. The spin–orbit splitting in the ground state was refined and the complete set of 14N-hyperfine parameters determined for the first time.

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.

Direct measurement of the fine-structure interval of27Alin its ground2Pstate

The $J=\frac{3}{2}\ensuremath{\leftarrow}\frac{1}{2}$ fine-structure transition in atomic ${}^{27}\mathrm{Al}$ in its ground ${}^{2}P$ state has been detected in the laboratory by far-infrared laser magnetic resonance. The fine-structure interval has been measured accurately as 3359.6228(17) GHz or 112.064 95(6) ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The spectra show the hyperfine structure associated with a nuclear spin of $\frac{5}{2}$ for ${}^{27}\mathrm{Al}.$ The splittings are well reproduced by the hyperfine parameters determined earlier by atomic beam methods. The analysis of the laser magnetic-resonance spectra casts doubt on the published value for the Zeeman parameter ${g}_{3/2}$ also from the atomic beam measurements. Although the value determined in this paper is intrinsically much less accurate, it is in better agreement with the value obtained by a completely independent theoretical calculation.

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.

The Far-Infrared Laser Magnetic Resonance Spectrum of CH2F

Far-infrared laser magnetic resonance (FIR-LMR) spectra due to the CH2F radical have been recorded on seven laser lines at wavelengths between 301 and 568 μm. Observed resonances were assigned to fine and hyperfine components of pure rotational transitions of CH2F in the ground vibrational state and the first excited state of the ν4out-of-plane bending mode. All assigned transitions obeya-dipole selection rules. The data were combined with previously reported microwave results (Y. Endo, C. Yamada, S. Saito, and E. Hirota,J. Chem. Phys.79, 1605 (1983)) and subjected to a least-squares fit to determine the parameters of the effective Hamiltonian describing thev4= 0 and 1 vibrational levels of the CH2F radical.

Fine-structure spectrum of the FO radical, observed by far-infrared laser magnetic resonance

The fine-structure transition Π1/22←2Π3/2 of the free radical FO has been detected by far-infrared laser magnetic resonance. All the observed transitions are magnetic dipole in character. The spin–orbit constant A0 has been determined experimentally; its value of −196.108 686(50) cm−1 is consistent with previous estimates. The analysis of a set of 290 transitions leads to the determination of a number of molecular parameters including rotational, centrifugal distortion, spin–orbit, lambda-doubling, magnetic hyperfine, and Zeeman terms. All four magnetic hyperfine structure constants a, bF, c, d for the F19 nucleus have been determined and are discussed in terms of the expectation values of the appropriate operators over the electronic wave function.

Fe+in its Ground6DState: A Direct Measurement of theJ= 1/2–3/2 andJ= 3/2–5/2 Fine‐Structure Intervals

The J = 1/2-3/2 and 3/2-5/2 fine-structure transitions in the atomic ion Fe+ in its ground 6D state have been detected in the laboratory by far-infrared laser magnetic resonance at 87 and 51 μm. The fine-structure intervals have been measured accurately by extrapolation to zero magnetic field as 3430.7762 (19) and 5843.7984 (12) GHz, respectively.

Measurement of high-frequency rotational transitions of H2O+ in its ground state by far-infrared laser magnetic resonance (LMR) spectroscopy

Thirteen new rotational transitions of H2O+ in the (0,0,0) level of the X̃ 2B1 state have been measured in the wavenumber region between 80 and 200 cm−1 (50 and 120 μm) by far-infrared laser magnetic resonance (LMR) spectroscopy. LMR data measured previously between 25 and 90 cm−1 (110 and 400 μm), as well as optical and infrared combination differences, have been combined with the new LMR data in a weighted least-squares analysis using an A-reduced expression of the rotational-fine structure Hamiltonian. Thirty-two molecular constants were simultaneously determined, some sextic centrifugal distortion parameters and some quartic and sextic spin-rotation parameters for the first time. From this improved set of molecular parameters, very accurate calculations of rotational term values and zero-field predictions of the 111–000 transition, including hyperfine structure, have been performed. Moreover, the electronic g-tensors and the hyperfine coupling constants are consistent with ab initio calculations which had been carried out for these constants.

Kinetics of the reactions of HCO with H and D atoms

AbstractThe rate constants for the reactions HCO+H → products (1) and HCO+D → products (2) were determined at room temperature in an isothermal discharge flow reactor. Atom and radical concentrations in the reactions were monitored using Electron Paramagnetic Resonance (EPR) for H and D atoms and Far Infrared Laser Magnetic Resonance (FIR‐LMR) and Laser Induced Fluorescence (LIF) for HCO. The overall rate constants describing the decay of the HCO concentrations with H and D, respectively, were found to be k1=(6.8±2.0)×1013 cm3 mol−1 s−1 and k2=(8.3±2.5)×1013 cm3 mol−1 s−1. The results are discussed assuming a mechanism that allows for parallel reaction pathways via a direct H atom abstraction reaction or via an addition‐elimination reaction through a short‐lived highly vibrationally excited formaldehyde complex.