Laser Magnetic Resonance Research Articles

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.

Magnetic Resonance-Guided Laser-Induced Thermotherapy of Recurrent Head and Neck Tumors

This article summarizes innovative laser methods to treat local tumors in the head and the neck and describes the technical details of the laser system and magnetic resonance thermometry. The specific techniques and results of this treatment are described.

Photoacoustic laser magnetic resonance

A new method of detecting laser magnetic resonance in the gas phase that employs the measurement of a modulated photoacoustic signal is reported in this Letter. The technique is applied to a study of the NO 2 spectrum using both light intensity and laser cavity frequency modulation. The method is demonstrated to have higher sensitivity than the usual absorption techniques.

The infrared spectrum of FeH2, studied in the gas phase by laser magnetic resonance

The infrared spectrum of the FeH2 radical in the gas phase has been studied in detail between 1605 and 1730 cm−1, by the technique of carbon monoxide laser magnetic resonance. The molecule is formed in an electric discharge through a mixture of H2 and Fe(CO)5 in helium. Many resonances are observed and assigned to transitions in the fundamental band of the antisymmetric stretching vibration 301 and in the associated hot band 211301. In the latter case, each vibrational level is split into two vibronic components. The measurements are used to determine the parameters of an effective Hamiltonian which is capable of modeling the data to within experimental error. The values determined for the band origin and zero-point vibrational constant are: ν3=1674.7203(3) cm−1 and B0=3.075 23(5) cm−1. The data show that the molecule is linear in its ground state and are consistent with an assignment of this state as 5Δg.

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.

99/00089 Study on removal of organic sulfur compound by modified activated carbon

A theoretical description of the Zeeman effect in a diatomic molecule is given on the basis of exact numerical diagonalization of the perturbation matrix. In this way it is also possible to include the fine and hyperfine structures to the desired degree of accuracy, and this is highly important for a complete theory of the molecular Zeeman effect. The present paper gives matrix elements for the Zeeman Hamiltonian which cover all types of valence states in a diatomic molecule. The molecular parameters are determined by a weighted nonlinear least-squares fit which includes electron paramagnetic resonance and laser magnetic resonance as well as zero-field data. Hence, the present method yields a direct determination of the basic molecular g-factors instead of effective ones for each rotational level. The 2Π ground states of OH and SH serve as test examples. Fitted values for gl + 1/2gs are 2.00092(3) and 2.000889(4) for OH and SH, respectively, while the respective theoretical ones are 2.00087 and 2.000951.

A link between vasomotion and spontaneous oscillations of oxygen in rat brain.

Early recordings with oxygen electrodes show that under steady state conditions, tissue oxygen tension (Po2) undergoes spontaneous fluctuations (Clark, 1958; Cooper et al., 1966; Hardwick, 1996; Misrahy et al, 1962). These oscillations differ between organs and species but a general pattern of l–10c/min with an amplitude of 10–30% of the mean Po2 has been observed (Morita-Tsuzuki et al., 1992; Hasibeder et al., 1994; Braun et al., 1992; Eickhoff and Jacobsen, 1982; Towell et al., 1976; Manil et al., 1984). Recordings of oscillations in flowmotion by other methods such as laser Doppler and magnetic resonance imaging (MRI) (Beinder et al, 1994; Morita-Tsuzuki et al., 1992; Hudetz et al., 1992; Biswal and Hudetz, 1996; Ren et al., 1993; Biswal et al., 1995, 1996) appear to exhibit similar frequencies of oscillation as the Po2.

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.

Rate constant for the reaction CH3+CH2(X̃3B1) at 298 K

AbstractThe rate constant for the reaction between CH3 and CH2 (X̃3B1 = 3CH2) radicals, was determined at T=298 K and p=1.33 mbar in an isothermal discharge flow reactor. Far Infrared Laser Magnetic Resonance (FIR‐LMR) was employed for monitoring 3CH2 and CH3 radical concentration‐versus‐time profiles. CH3 was determined in the form of NO via the conversion reaction CH3+NO2 → CH3O+NO. The CH3 and 3CH2 radicals were generated by the reactions F+CH4 → CH3+HF and F+CH3 → 3CH2+HF. The rate constant for the recombination reaction was determined together with the rate constant for reaction (1). The measurements gave a rate constant value for reaction (1) of k1 = (6.5±1.2)·1013 cm3/mol s.

Faraday Laser Magnetic Resonance Spectroscopy of Vibrationally Excited C2D

We studied the gas phase spectrum of the deuterated ethynyl radical C2D in the region between 3196 and 3243 cm−1using a Faraday LMR spectrometer in combination with a CO overtone laser. The C2D radicals were generated in a dc glow discharge containing helium, deuterium, and acetylene. We observed a hot band between two vibronic2Π states with an origin at 3225 cm−1. The lower level is assigned to the first excited bending level of the electronicXground state. The upper level corresponds to the first excited electronic stateAat 3513 cm−1, which was observed previously [J. Mol. Struct.190,41–60 (1988)]. This region is subject to strong vibronic interaction, caused by mixing of the electronicXground state with theAstate at 3513 cm−1. From the analysis of the spectra we could determine the orbitalgfactor of the upper level, which gave important information about the mixing ratios. In addition we were able to derive a precise term value for the first excited bending level of the electronicXground state. The experimentally derived molecular parameters are compared with theoretically calculated values, obtained byab initiocalculations.

Collisions of O(1D) with HF, F2, XeF2, NF3, and CF4: Deactivation and reaction

The reactions of O(1D) atoms with fluorides have been investigated by time-resolved laser magnetic resonance (LMR). O(1D) atoms were produced by the dissociation of ozone with an excimer laser (KrF, 248 nm). By monitoring Cl atoms (when HCl or Cl2 is added) or FO radicals, the rate constants for total removal of O(1D) (×10−11 cm3/s) by HF(5.1±1.0), F2(0.81±0.20), XeF2(16±3.0), NF3(1.2±0.25), and CF4(<0.016) have been determined at 298 K. Reaction rate constants (×10−11 cm3/s) have been obtained for HF(1.5±0.3), F2(0.81±0.2), XeF2(14±3.0), and NF3(1.0±0.3). The deactivation of O(1D) by HX (X=F, Cl, Br) is discussed. Ab initio calculations have been performed with the aim of qualitative comparison of deactivation of O(1D) by F2 and Cl2.

A direct investigation of the reaction CH3+OH: Overall rate constant and CH2 formation at T=298 K

AbstractThe rate constant and the product distribution of the reaction CH3+OH r̊ products (1) were studied at room temperature over a range of pressures (0.7 mbar ≤p≤467 mbar) with M= He as inert bath gas. At pressures of 45 to 467 mbar, towards the high pressure range of the reaction, experimental determinations were performed using the laser flash photolysis technique with transient UV absorption spectrometry (LFP/TAS) for direct monitoring of the CH3 and OH radicals. In this range, the overall rate constant for the reaction was found to be practically independent of pressure at k1 (298 K)=(4.4±0.8)x1013 cm3 mol−1 s−1. At pressures of 0.7 mbar to 4.0 mbar, the reaction was studied using the discharge flow (DF) technique with laser magnetic resonance (LMR) for the direct detection of the reactants CH3 and OH and the reaction product CH2. The measured overall rate constants at the low pressures were found to increase slightly with increasing pressure and approach the value at “high” pressure from the LFP/TAS experiments. From simulations of the measured concentration‐versus‐time profiles of the CH3, OH, and CH2 radicals, the branching ratio for the reaction channel CH3+OHr̊ CH2+H2O (1.1) was determined at p=1.33 mbar, T=298 K to be k1.1lk1=(0.89±0.09). Implications of the results are discussed considering the fall‐off curve for the reaction, the reaction mechanism and the product distribution, and the available thermochemical data.

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.

First observation of ro-vibrational transitions of the SiC radical by infrared LMR spectroscopy

Ro-vibrational transitions in the (1–0) band of the electronic ground state X 3Π of the SiC radical have been observed with high accuracy using CO 2-Faraday laser magnetic resonance (LMR) spectroscopy. The molecule parameters of this electronic state were determined in a nonlinear least-squares fit including all relevant experimental data of earlier work. No indication for a perturbation by other electronic states could be found. For the band origin of the fundamental band we obtained 953.32062(27) cm −1.

The 248 nm photodissociation of ClF 3: quantum yields for F and Cl atoms

The dynamics of the 248 nm excimer-laser-induced photodissociation of ClF 3 has been investigated by the observation of the Cl atoms by time-resolved laser magnetic resonance. In the presence of Cl 2, photolytically produced F atoms interacted with Cl 2 to produce Cl atoms. Quantum yields for F and Cl atom formation were measured by comparison to the Cl signal from COCl 2 photolysis for which the quantum yield is known in the literature. The quantum yields for F and Cl atom formation are determined to be 1.85 −0.25 +0.15 and <0.02, respectively. By examination of the electronic configuration of the excited state of ClF 3, the primary photodissociation products are predicted to be ClF 2+F.

Far Infrared Laser Magnetic Resonance Detection of CF3, CHF2, and CH2F

AbstractFar infrared laser magnetic resonance (FIR‐LMR) spectra of CF3, CHF2, and CH2F radicals were observed in the 300–800 μm wavelength region in the reactions of F atoms with a series of different hydrocarbon and partially fluorinated hydrocarbon molecules. To identify the carriers of the observed resonance patterns and to exclude or identify contamination of the spectra by additional resonances from other paramagnetic species, numerous chemical tests were developed and performed. With optimized sources and the chemical tests in hand, many spectra could be unambiguously attributed to CF3, CHF2, and CH2F, respectively. The present study reports the first gas phase detection of CHF2 radicals in their ground electronic state.

The NCN 211310Hot Band Measured by Infrared Laser Magnetic Resonance Spectroscopy

The NCN 211310Hot Band Measured by Infrared Laser Magnetic Resonance Spectroscopy