- ID:
- ivo://CDS.VizieR/J/A+A/563/A137
- Title:
- THz spectrum of methylamine
- Short Name:
- J/A+A/563/A137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Methylamine (CH_3_NH_2_) is the simplest primary alkylamine and has been detected in the interstellar medium. The molecule is relatively light, with the 50K Boltzmann peak appearing near 800GHz. However, reliable predictions for its rotational spectrum are available only up to 500GHz. Spectroscopic analyses have been complicated by the two large amplitude motions: internal rotation of the methyl top and inversion of the amino group. The aims is to provide reliable predictions of the methylamine ground state rotational spectrum above 500GHz we studied its rotational spectrum in the frequency range from 500 to 2650GHz. The spectra of methylamine were recorded using the spectrometers based on Schottky diode frequency multiplication chains in the Lille laboratory (500-945GHz) and in JPL (1060-2660GHz). The analysis of the rotational spectrum of methylamine in the ground vibrational state was performed on the basis of the group-theoretical high barrier tunneling Hamiltonian developed for methylamine by Ohashi and Hougen. In the recorded spectra we have assigned 1849 new rotational transitions of methylamine. They were fitted together with previously published data to a Hamiltonian model that uses 76 parameters with overall weighted rms deviation of 0.87. On the basis of the new spectroscopic results, predictions of transition frequencies in the frequency range up to 3THz with J<50 and Ka<20 are presented.
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- ID:
- ivo://CDS.VizieR/J/AJ/146/97
- Title:
- Ti line list for the Lick hallow-cathode lamp
- Short Name:
- J/AJ/146/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the wavelength calibration of the Hamilton echelle spectrograph (the Lick observatory). The main problem of the calibration arises from the fact that thorium lines are absent in the spectrum of ThAr hollow-cathode lamp now under the operation. On the other hand, numerous unknown strong lines are present in the spectrum. These lines was identified with titanium. We estimate the temperature of the lamp gas which permits us to calculate the intensities of the lines, and to select a large number of relevant TiI and TiII lines. The titanium line list for the Lick hallow-cathode lamp is presented. The wavelength calibration using this line list was made with accuracy about 0.006{AA}.
- ID:
- ivo://CDS.VizieR/J/ApJS/228/11
- Title:
- Time-dependent cooling in photoionized plasma
- Short Name:
- J/ApJS/228/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I explore the thermal evolution and ionization states in gas cooling from an initially hot state in the presence of external photoionizing radiation. I compute the equilibrium and nonequilibrium cooling efficiencies, heating rates, and ion fractions for low-density gas cooling while exposed to the ionizing metagalactic background radiation at various redshifts (z=0-3), for a range of temperatures (10^8^-10^4^K), densities (10^-7^-10^3^cm^-3^), and metallicities (10^-3^-2 times solar). The results indicate the existence of a threshold ionization parameter, above which the cooling efficiencies are very close to those in photoionization equilibrium (so that departures from equilibrium may be neglected), and below which the cooling efficiencies resemble those in collisional time-dependent gas cooling with no external radiation (and are thus independent of density).
- ID:
- ivo://CDS.VizieR/J/A+A/520/A64
- Title:
- Trans-HCOOH hyperfine structure
- Short Name:
- J/A+A/520/A64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Formic acid, HCOOH, is the simplest organic acid and the first that has been identified in the interstellar medium. Its astrophysical relevance has motivated this spectroscopic study. The aim of this investigation is to provide very accurate rest frequencies for the trans isomer of HCOOH as well as to improve the spectroscopic and hyperfine parameters available in the literature for this molecule. The Lamb-dip technique has been exploited in order to record the rotational spectrum of trans-HCOOH at sub-Doppler resolution in the millimeter- and submillimeter-wave frequency ranges and, when possible, to resolve the hyperfine structure due to the hydrogen nuclei. THz measurements have been carried out as well. The experimental investigation has been supported by high-level quantum-chemical calculations.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A167
- Title:
- Transition data of E1 transitions for PII
- Short Name:
- J/A+A/622/A167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The main goal of this paper is to present accurate and extensive transition data for the PII ion. These data are useful in various astrophysical applications. The multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic configuration interaction (RCI) methods, which are implemented in the general-purpose relativistic atomic structure package GRASP2K, were used in the present work. In the RCI calculations the transverse-photon (Breit) interaction, the vacuum polarization, and the self-energy corrections were included. Energy spectra are presented for 48 even states of the 3s^2^3p^2^, 3s^2^3p{4p, 4f, 5p, 5f, 6p}, 3s3p^2^3d configurations, and for 58 odd states of the 3s3p^3^, 3s^2^3p{3d, 4s, 4d, 5s, 5d, 6s} configurations in the PII ion. Electric dipole (E1) transition data are computed between these states along with the corresponding lifetimes. The average uncertainty of the computed transition energies is between five and ten times smaller than the uncertainties from previous calculations. The computed lifetimes for the 3s^2^3p4s^3^P^o^ states are within the error bars of the most current experimental values.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A82
- Title:
- Transition data of E1 transitions for the CeIV
- Short Name:
- J/A+A/658/A82
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We present extensive energy level and transition data for the Ce IV spectrum. By providing accurate atomic data, we evaluate the impact of atomic data on the opacity in the neutron star merger ejecta. We performed energy spectra and transition data calculations using the GRASP2018 package, which is based on the multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods, and the HULLAC code, which is based on a parametric potential method. We present energy spectra calculated for the 225 levels for the Ce^3+^ ion. Energy levels are compared with recommended values from the NIST Atomic Spectra Database and other available works. The root-mean-square (rms) deviations obtained for the GRASP2018 energy levels of the 5p^6^nl configurations from the NIST data are 1270cm^-1^. The rms deviations for the HULLAC results from the NIST data are 5780cm^-1^. Furthermore, electric dipole (E1) transition data, line strengths, weighted oscillator strengths, and transition rates are computed between the above levels. The computed transition rates are compared with other theoretical computations. We also evaluate the accuracy of the wave functions and transition parameters by analyzing the dependencies of the line strength S on the gauge parameter G. The gauge dependency method also allows us to determine the transitions for which the ratio between the Babushkin and Coulomb gauges shows real agreement between forms and the transitions for which the agreement between both gauges is random. Using the GRASP2018 and HULLAC data, the opacities in the neutron star merger ejecta are also calculated. We find that the opacity of CeIV is higher than that presented by previous works, which is because of the higher completeness of our atomic data. Although the differences in the energy levels and transition probabilities cause different features in the opacity spectrum, the Planck mean opacities of both data sets agree within 20%.
- ID:
- ivo://CDS.VizieR/J/ApJ/855/123
- Title:
- Transition frequencies of ethanimine (CH_3_CHNH)
- Short Name:
- J/ApJ/855/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Ethanimine, a possible precursor of amino acids, is considered an important prebiotic molecule and thus may play important roles in the formation of biological building blocks in the interstellar medium. In addition, its identification in Titan's atmosphere would be important for understanding the abiotic synthesis of organic species. An accurate computational characterization of the molecular structure, energetics, and spectroscopic properties of the E and Z isomers of ethanimine, CH_3_CHNH, has been carried out by means of a composite scheme based on coupled-cluster techniques, which also account for extrapolation to the complete basis-set limit and core-valence correlation correction, combined with density functional theory for the treatment of vibrational anharmonic effects. By combining the computational results with new millimeter-wave measurements up to 300GHz, the rotational spectrum of both isomers can be accurately predicted up to 500GHz. Furthermore, our computations allowed us to revise the infrared spectrum of both E- and Z-CH_3_CHNH, thus predicting all fundamental bands with high accuracy.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/141
- Title:
- Transition frequencies of MN and DMN
- Short Name:
- J/ApJ/805/141
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-resolution pure rotational spectra of four alkylnaphthalenes were measured in the range of 6-15GHz using a molecular-beam Fourier-transform microwave spectrometer. Both a- and b-type transitions were observed for 1-methylnaphthalene (1-MN), 1,2-dimethylnaphthalene (1,2-DMN), and 1,3-dimethylnaphthalene (1,3-DMN); only a-type transitions were observed for 2-methylnaphthalene (2-MN). Geometry optimization and vibrational analysis calculations at the B3LYP/6-311++G(d,p) level of theory aided in the assignments of the spectra and the characterization of the structures. Differences between the experimental and predicted rotational constants are small, and they can be attributed in part to low-lying out-of-plane vibrations, which distort the alkylnaphthalenes out of their equilibrium geometries. Splittings of rotational lines due to methyl internal rotation were observed in the spectra of 2-MN, 1,2-DMN, and 1,3-DMN, and allowed for the determination of the barriers to methyl internal rotation, which are compared to values from density functional theory calculations. All four species are moderately polar, so they are candidate species for detection by radio astronomy, by targeting the transition frequencies reported here.
- ID:
- ivo://CDS.VizieR/J/A+A/416/383
- Title:
- Transition probabilities for Fe XVIII
- Short Name:
- J/A+A/416/383
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Energy levels and the corresponding transition probabilities as well oscillator strengths and line strengths for allowed (E1) and forbidden (E2, M1) transitions among the lowest 379 levels of fluorine-like Fe XVIII are presented. Calculations were performed using the multiconfigurational Dirac-Fock GRASP code.
- ID:
- ivo://CDS.VizieR/J/ApJS/169/120
- Title:
- Transition probabilities for HfII and Hf
- Short Name:
- J/ApJS/169/120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Radiative lifetimes from laser-induced fluorescence measurements, accurate to ~+/-5%, are reported for 41 odd-parity levels of HfII (Z=72). The lifetimes are combined with branching fractions measured using Fourier transform spectrometry to determine transition probabilities for 150 lines of HfII. Approximately half of these new transition probabilities overlap with recent independent measurements using a similar approach. The two sets of measurements are found to be in good agreement for lines in common. Our new laboratory data are applied to refine the hafnium photospheric solar abundance and to determine hafnium abundances in 10 metal-poor giant stars with enhanced r-process abundances. For the Sun we derive log{epsilon}(Hf)=0.88+/-0.08 from four lines; the uncertainty is dominated by the weakness of the lines and their blending by other spectral features. Within the uncertainties of our analysis, the r-process-rich stars possess constant Hf/La and Hf/Eu abundance ratios, log{epsilon}(Hf/La)=-0.13+/-0.02 ({sigma}=0.06) and log{epsilon}(Hf/Eu)=+0.04+/-0.02 ({sigma}=0.06). The observed average stellar abundance ratio of Hf/Eu and La/Eu is larger than previous estimates of the solar system r-process-only value, suggesting a somewhat larger contribution from the r-process to the production of Hf and La. The newly determined Hf values could be employed as part of the chronometer pair, Th/Hf, to determine radioactive stellar ages.
