Spin-rotational Parameters Research Articles

Re-appraisal of the hyperfine-structure constants in YbF: relativistic configuration interaction approach

Ab initio calculation of the spin rotational Hamiltonian parameters A and Ad has been performed using a fully-relativistic restricted active space (RAS) configuration interaction (CI) method for the YbF molecule. These calculations lead to the results for the hyperfine-structure constants as A = 6725 MHz, and Ad = 86 MHz, which agree favorably well with some previous correlated calculations and experimental findings. The convergence behavior of the parameters A and Ad with respect to the size of the active space and basis set has been tested satisfactorily for the reliability of the present results (within an uncertainty of ∼7%). Further, we believe that the theoretical estimates of some symmetry violating interaction constants like Wd can also be predicted with similar accuracy using the RASCI method.

Determination of molecular hyperfine-structure constant using the second-order relativistic many-body perturbation theory

The spin-rotational Hamiltonian parameters ${A}_{\ensuremath{\parallel}}$ and ${A}_{\ensuremath{\perp}}$ for the BaF molecule are calculated using four-component relativistic spinors at the second-order many-body perturbation theory (MBPT) level via the Z-vector technique. The second-order MBPT is applied to assess the accuracy of the computed hyperfine-structure constants before studying the problem with the state-of-the-artcoupled cluster with single and double excitations (CCSD) method which is highly accurate but computationally more expensive than MBPT. The hyperfine-structure constants $A$ and ${A}_{d}$ resulted from these calculations agree favorably well with experimental findings and with other correlated calculations. The convergence behavior of $A$ and ${A}_{d}$ with respect to the number of active orbitals used in the perturbative calculations suggests that our estimated $A$ and ${A}_{d}$ values should be accurate.

The rotational spectrum of the NF 2 free radical: Determination of molecular structure

Many rotational transitions of nitrogen difluoride, NF 2, have been recorded in the millimetre-wave region. By fitting the present and previous data together, it has been possible to determine several higher order centrifugal distortion terms and so refine the rotational and spin-rotational parameters. In addition, it has been possible to determine the off-diagonal electron spin–nuclear spin coupling parameter T ab for the two equivalent 19F nuclei. This term causes ortho– para mixing and, to our knowledge, this is the first time that such a term has been determined directly by spectroscopic means for spin 1/2 nuclei. Density- and wave-functional calculations employing moderately large to large basis sets have been carried out to test the reliability of such calculations and to corroborate the experimental hyperfine structural findings. In addition, vibration–rotation interaction terms were calculated theoretically in order to derive a mixed experimental/ ab initio equilibrium structure for NF 2 in the X 2B 1 state, namely: r = 134.691 ( 68 ) pm and ∠ = 103.132 ( 20 ) ° .

Fourier transform microwave spectroscopy of the isocyanomethyl radical, CH2NC

The pure rotational spectrum of the isocyanomethyl radical, CH(2)NC, was measured for the first time by using a Fourier transform microwave spectrometer. The molecule was produced by a discharge of isocyanomethane, CH(3)NC, diluted in Ar or Ne. The spectral lines due to the N=1-0 and 2-1 transitions were recorded near 22 and 44 GHz, respectively. The observed spectrum showed a complicated fine and hyperfine structure because of the same order of interaction energies. Among the 39 spectral lines detected and assigned, the transitions with K(a)=1 show no hyperfine splitting due to the hydrogen nuclei, suggesting planarity for the molecule. Molecular constants such as rotational and spin-rotational parameters including centrifugal effects and hyperfine coupling constants due to both the nitrogen and the hydrogen nuclei were accurately determined. The structure and the astronomical implications of the molecule are discussed.

Observation and analysis of the infrared spectra of O2–HF near 3950 cm−1 and O2–DF near 2900 cm−1

Spectra were recorded in the H–F stretching fundamental region for O2–HF and in the D–F region for O2–DF, using a laser difference-frequency spectrometer coupled to a slit-nozzle expansion. By varying the ratio of oxygen to carrier gas, beam temperatures ranging from 5 to 16 K were obtained. One standard uncertainty for the relative frequency position of unblended lines is 0.0001 cm−1. Each spectrum was visually subdivided into a stronger (cold) spectrum and a weaker (hot) spectrum. Lines in the cold spectrum were fit to nearly experimental error, using a rotational Hamiltonian for open-shell complexes taken from the literature. For O2–DF, 21 rotational and spin–rotational parameters (10 each for the upper and lower state plus the band origin) were used to fit 86 transitions to a standard deviation of 0.0002 cm−1. For O2–HF, 23 rotational and spin–rotational parameters were used to fit 83 transitions to a standard deviation of 0.0003 cm−1. The slightly poorer quality of the fit for O2–HF than for O2–DF is probably related to the somewhat larger vibrational amplitudes expected for the van der Waals motions in the protonated species. In spite of strenuous efforts, a simultaneous global fit to measurement error of the eight cold-spectrum branches and fourteen hot-spectrum branches could not be achieved, suggesting some improvement in the model used to derive the fitting Hamiltonian may be necessary.

Enhancement of the electric dipole moment of the electron in the BaF molecule

We report results of ab initio calculation of the spin-rotational Hamiltonian parameters including $P$- and $P,T$-odd terms for the BaF molecule. The ground-state wave function of BaF molecule is found with the help of the relativistic effective core potential method followed by the restoration of molecular four-component spinors in the core region of barium in the framework of a nonvariational procedure. Core polarization effects are included with the help of the atomic many-body perturbation theory for the Barium atom. For the hyperfine constants the accuracy of this method is about 5--10 %.

P,T-Odd Spin-Rotational Hamiltonian for YbF Molecule.

An {ital ab} {ital initio} relativistic effective core potential calculation of electronic wave function for the ground state ({sup 2}{Sigma}) of a YbF molecule is carried out followed by the restoration of molecular four-component spinor behavior in the core region of ytterbium in the framework of a nonvariational procedure. The constructed spinors are used to evaluate the spin-rotational Hamiltonian parameters including {ital P}- and {ital P},{ital T}-odd terms of the molecule. {copyright} {ital 1996 The American Physical Society.}

High precision measurements of hyperfine structures near 790 nm of I 2

High precision measurements of hyperfine splittings of rovibrational lines of the (ν′-ν″)=(0–15) band of the B0 u + — X0 g + transition of I 2 were performed in the near infrared around 790 nm using spectrally narrowed diode lasers. Rotational states with J″ between 0 and 99 were investigated and hyperfine parameters could be derived for the two electronic states separately. For the first time the rotational variation of the quadrupole and the spin-rotational hyperfine coupling parameters could be determined for I 2. A relation is given, by which the hyperfine parameters for a rotational line of the (0–15) band can be predicted, and by which hyperfine splittings of this band can be calculated with an uncertainty of less than 100 kHz for 16 ≤ J″ ≤ 99.

Enhancement of the electric dipole moment of the electron in the YbF molecule.

We report results of ab initio calculation of the spin-rotational Hamiltonian parameters including P- and P,T-odd terms for the BaF molecule. The ground-state wave function of BaF molecule is found with the help of the relativistic effective core potential method followed by the restoration of molecular four-component spinors in the core region of barium in the framework of a nonvariational procedure. Core polarization effects are included with the help of the atomic many-body perturbation theory for the Barium atom. For the hyperfine constants the accuracy of this method is about 5-10 %. [S1050-2947(97)50311-8].

The rotational spectrum of trans-HOCO and DOCO

Part of the rotational spectrum of the hydroxyformyl radical, HOCO, and its deuterated analog has been detected at frequencies between 230 and 300 GHz. The radical was formed in a flow system by the reaction between chlorine atoms and formic acid. Analysis of the spectra yields reliable estimates of the rotational, centrifugal distortion and spin–rotational parameters describing the ground state of this species. The rotational constants derived for HOCO and DOCO are consistent with a planar equilibrium structure and are used to confirm that the carrier of the spectrum is the trans-geometrical isomer.

Calculation of the spin-rotational Hamiltonian including P- and P, T-odd weak interaction terms for HgF and PbF molecules

The spin-rotational Hamiltonian parameters for the ground states of HgF and PbF molecules are evaluated on the basis of the ab initio effective core potential calculations. The term corresponding to the electric dipole moment of the electron as well as several other P- and P, T-odd terms are included.

A determination of the spin–rotation parameters for NO2 in the X̃ 2A1 state by microwave–optical double resonance

Magnetic dipole transitions between the spin components of rotational levels of NO2 in its ground state have been observed by the technique of microwave–optical double resonance. Fluorescence induced by an argon ion laser was used to monitor the process. Observations were made in the range 4 to 12 GHz and provide information on levels with a wide spread of N and Ka values. The results have been used in conjunction with the known electric dipole transition frequencies and some recent data from radio frequency–infrared double resonance to determine the rotational and spin–rotational parameters for the molecule in its ground state. It has proved possible to determine all the three quadratic and six quartic parameters in the spin–rotational Hamiltonian. The improvement in knowledge of the spin–rotation intervals allow a refinement of the Zeeman parameters for NO2 by refitting the data from the EPR and LMR spectra. The results are in good agreement with the relationships gSaa = gS−eaa/2Baa, etc.

Rotational and hyperfine parameters of NH 2(X 2B 1) from LMR spectra

Seventeen rotational transitions up to N=7 of the NH 2 radical in its ground vibronic state have been measured by far infrared laser magnetic resonance spectroscopy. Analysis of the Zeeman patterns and hyperfine structure yields precise rotational, spin-rotational and distortion parameters, and isotropic and anisotropic hyperfine interaction parameters for both 14N and 1H nuclei.