Adiabatic Polarization-Transfer Methods in MAS Spectroscopy

Astronomy & Astrophysics, 2020

Context. Astronomical masers have been effective tools in the study of magnetic fields for years. Observations of the linear and circular polarisation of different maser species allow for the determination of magnetic field properties, such as morphology and strength. In particular, methanol can be used to probe different parts of protostars, such as accretion discs and outflows, since it produces one of the strongest and the most commonly observed masers in massive star-forming regions. Aims. We investigate the polarisation properties of selected methanol maser transitions in light of newly calculated methanol Landé g-factors and in consideration of hyperfine components. We compare our results with previous observations and evaluate the effect of preferred hyperfine pumping and non-Zeeman effects. Methods. We ran simulations using the radiative transfer code, CHAMP, for different magnetic field values, hyperfine components, and pumping efficiencies. Results. We find a dependence be...

Journal of Quantitative Spectroscopy and Radiative Transfer, 2017

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Journal of Molecular Structure: THEOCHEM, 2006

The evaluation of the first and second derivative of the non adiabatic coupling between the several 1 R + adiabatic states of LiH, RbH and CsH molecules, is considered from accurate diabatic and adiabatic data. Such derivatives of the electronic wave function are determined through a numerical differentiation of the rotational matrix connecting the diabatic and adiabatic representations. The first as well as the second derivative presents many peaks, related to ionic-neutral and neutral-neutral coupling between the 1 R + states. Such radial coupling has been exploited to calculate the first adiabatic correction, which corresponds to the diagonal term of the second derivative divided by the reduced mass, for the ground and some excited states of the three molecules. The second adiabatic correction has been determined using the Virial theorem.

The Journal of Organic Chemistry, 1990

Microdischarges at moderate to high pressure in argon were investigated. A hole opening diameter of 500 µm direct current (dc) microhollow cathode discharges (MHCD) were characterized by electrical measurements and optical emission spectroscopy (OES) for pressures ranging between 90 and 800 Torr and current from 5 to 20 mA. Current-voltage characteristic curves were obtained as a function of the pressure for this hole diameter. MHCD enables stable dc discharges for molybdenum electrodes material at constant Ar + 2%H 2 flow of 0.03 /min. Optical emission spectroscopy and analysis of the spectral line broadening of plasma line emissions were performed in order to measure gas discharge parameters. Electron number densities were obtained from H β Balmer line (∼ 10 14 cm −3). For the above mentioned discharge conditions, gas temperature was estimated to be 550-850 K from OH rotational bands. Excitation temperature was measured based on two lines method (from atomic Mo lines) and from 4p-4s and 5p-4s Ar radiative transitions. Hydrogen atom temperature was measured for 800 Torr (∼ 12000 K).

The Journal of Physical Chemistry A, 2008

Vertical and adiabatic excitation energies and oscillator strengths for valence and Rydberg states of hydroxycarbene (HCOH) and methylhydroxycarbene (CH 3 COH) are reported. The electronic properties were computed with equation-of-motion coupled-cluster methods with single and double substitution methods (EOM-CCSD) and the aug-cc-pVTZ basis set. The states' characters were analyzed by plotting natural transition orbitals (NTOs). The calculations demonstrate that the shape, size, and energy of each Rydberg orbital are affected to varying degrees by their interaction with the ion core. Likewise, the corresponding quantum defects reflect the Rydberg electron−ion core interactions. The results reported herein, combined with previously reported calculations of the photoelectron spectrum of HCOH, should help in designing strategies for state-selective detection of hydroxycarbenes via ionization.

The reverse-DADI method: Computation of frequency-dependent atomic polarizabilities for carbon and hydrogen atoms in hydrocarbon structures, 2024

A specific method, combining some ingredients of the well-known DDA and PDI approaches, has been developed in our group since many years to calculate the absorption cross-sections of carbonaceous nanoparticles based on their atomistic details. This method, here named the Dynamic Atomic Dipole Interaction (DADI) model, requires the knowledge of the position and frequency-dependent polarizability of each atom constituting the nanoparticles. While the atomic positions can be quite easily obtained, for example as the results of molecular dynamics simulations, obtaining the frequency-dependent atomic polarizabilities is a trickier task. Here, a fitting procedure, named the reverse-DADI method, has been applied to calculate the frequencydependent atomic polarizability values for carbon and hydrogen atoms involved in aromatic cycles or in aliphatic chains, on the basis of frequency-dependent molecular polarizabilities of various PAH and alkane molecules, calculated with the TD-DFT theory, in the UV-Visible range. Then, using these frequency-dependent atomic polarizabilities as input parameters in the DADI model has been shown to lead to an accurate representation of the absorption cross-sections of various PAH and alkane molecules with respect to the corresponding values obtained at the TD-DFT level, with however the great advantage of a much shorter time of calculations. Furthermore, these results are indications of a good transferability of the frequency-dependent atomic polarizability values obtained here to any C or H atom of any PAH or alkane molecule. This opens the way for building large databases of optical properties for carbonaceous species of atmospheric or astrophysical interests.

The geometries in the staggered and eclipsed conformations of the metallocenes, M(C 5 H 5 ) 2 with M ) Mn, Fe, Co, Ni, and Ru, have been calculated at the local and nonlocal density functional theory (LDFT and NLDFT) levels. The M-C distance is predicted to be too short at the LDFT level and too long at the NLDFT level. The doublet low-spin states for M ) Mn and Co show distortions away from the idealized fivefold symmetries. The low-spin state for M ) Mn is predicted to be lower in energy than the high-spin state in contrast to the observed experimental results. The size of the splitting is strongly dependent on the computational level. The values of R and γ were calculated for the various metallocenes. The highest value of γ was found for M ) Co. † Current address: Pacific

The Journal of Physical Chemistry A, 2005

The CIS and EOM-CCSD adiabatic geometries for the first excited states of a set of small molecules (C 2 H 4 , C 2 H 2 , H 2 CdO, H 2 CdS, CS 2 , CO 2 , SO 2 , NO 2 ) have been calculated using the 6-311++G** basis set to see if the former geometries can be good starting points for optimizations at the latter theoretical level. With most of the molecules, there is fairly good agreement between the results from the two methods, and EOM-CCSD gives good agreement with the available experimental data. A detailed discussion of the lowest-lying singlet excited states in CO 2 and CS 2 is presented, highlighting the pronounced differences in electronic character and equilibrium structure displayed by these isovalent species. The origins of the structural distortions that are frequently found for the adiabatic excited states are examined with the aid of deformation density plots and the electron localization function (ELF).