1,721,042 research outputs found
The high-resolution infrared spectrum of DC4H from 450 to 1100 cm−1: overtone, combination and hot bands.
No full textThe high-resolution infrared spectrum of monodeuterated diacetylene has been recorded in the 450–
1100 cm−1 spectral region by Fourier transform infrared spectroscopy. Seven new bands have been
identified: the ν3 fundamental (C–C stretch), and the ν8 + ν9, ν7 + ν8, 2ν7, 2ν8, ν8 + ν9 − ν9, and
ν6 + ν9 − ν9 combination, overtone, and hot bands. The assigned transitions, together with those
previously reported for the fundamental bands [F. Tamassia, L. Bizzocchi, C. Degli Esposti, L. Dore,
M. Di Lauro, L. Fusina, M. Villa, and E. Canè, Astron. Astrophys. 549, A38 (2013)], form a comprehensive
data set which comprises more than 2500 ro-vibrational transitions, and involves all singly
and most doubly excited vibrational states of DC4H lying below 1000 cm−1. Rotational and vibrational
l-type resonance effects among the sub-levels of excited bending states were considered in the
analysis, which also included a careful treatment of the various anharmonic interactions coupling
many vibrational states lying above 600 cm−1. Reliable and unambiguous spectroscopic parameters
were obtained for each investigated state, including the rotational and centrifugal distortion constants
Bv and Dv, the l-type doubling parameter qt, the anharmonicity constants xL(89), xL(69), and the vibrational
l-type terms r89, r69 for the v8 = v9 = 1 and v6 = v9 = 1 bend-bend combination states
Detection of N15NH+ in L1544
No full textContext. Excess levels of 15N isotopes which have been detected in primitive solar system materials are explained as a remnant of interstellar chemistry which took place in regions of the protosolar nebula.
Aims. Chemical models of nitrogen fractionation in cold clouds predict an enhancement in the gas-phase abundance of 15N-bearing molecules, thus we have searched for 15N variants of the N2H+ ion in L1544, which is one of the best candidate sources for detection owing to its low central core temperature and high CO depletion.
Methods. With the IRAM 30m telescope we have obtained deep integrations of the N15NH+ (1−0) line at 91.2 GHz.
Results. The N15NH+ (1−0) line has been detected toward the dust emission peak of L1544. The 14N/15N abundance ratio in N15NH+
resulted 446 ± 71, very close to the protosolar value of ∼ 450, higher than the terrestrial ratio of ∼270, and significantly lower than the lower limit in L1544 found by Gerin et al. (2009, ApJ, 570, L101) in the same object using ammonia isotopologues
Detection of 15NNH+ in L1544: non-LTE modelling of dyazenilium hyperfine line emission and accurate14N/15N values
Full text linkContext. Samples of pristine solar system material found in meteorites and interplanetary dust particles are highly enriched in 15N. Conspicuous nitrogen isotopic anomalies have also been measured in comets, and the 14N/15N abundance ratio of the Earth is itself higher than the recognised presolar value by almost a factor of two. Low-temperature ion/molecule reactions in the proto-solar nebula have been repeatedly indicated as being responsible for these 15N -enhancements.
Aims. We have searched for 15N variants of the N2H+ ion in L1544, a prototypical starless cloud core that is one of the best candidate sources for detection owing to its low central core temperature and high CO depletion. The goal is to evaluate accurate and reliable 14N/15N ratio values for this species in the interstellar gas.
Methods. A deep integration of the 15NNH+ (1−0) line at 90.4GHz was obtained with the IRAM 30m telescope. Non-LTE radiative transfer modelling was performed on the J = 1−0 emissions of the parent and 15N-containing dyazenilium ions, using a Bonnor-Ebert sphere as a model for the source.
Results. A high-quality fit of the N2H+ (1−0) hyperfine spectrum has allowed us to derive a revised value of the N2H+ column density in L1544. Analysis of the observed N15NH+ and 15NNH+ spectra yielded an abundance ratio N(N15NH+)/N(15NNH+) = 1.1 ± 0.3. The obtained 14N/15N isotopic ratio is ∼1000 ± 200, suggestive of a sizeable 15N depletion in this molecular ion. Such a result is not consistent with the prediction of the current nitrogen chemical models.
Conclusions. Since chemical models predict high 15N fractionation of N2H+, we suggest that 15N14N, or 15N in some other molecular form, tends to deplete onto dust grains
Accurate rotational rest-frequencies of CH2NH at submillimetre wavelengths
No full textMethanimine (CH2NH) has been detected in different astronomical sources, both galactic (as in several “hot cores”, the circumstellar enevolope IRC+10216, and the L183 pre-stellar core) and extragalactic, and is considered a pre-biotic interstellar molecule. Its ground-state rotational spectrum has been studied in the laboratory up to 172 GHz, well below the spectral ranges covered by Herschel/HIFI and the ALMA bands 9 and 10. In this laboratory study, we extend into the submillimetre-wave region the detection of the rotational spectrum of CH2NH in its vibrational ground state. The investigation was carried out using a source-modulation microwave spectrometer equipped with a cell coupled to a pyrolysis apparatus working at 1150 ◦C. The spectrum was recorded in the frequency range 329–629 GHz, with the detection of 58 transitions. The newly measured transition frequencies, along with those available from previous microwave studies, allow us to determine fairly accurate rotational constants of CH2NH and the complete sets of quartic and sextic centrifugal distortion constants, in addition to two octic constants. Several transitions have an hyperfine structure due to the 14N nucleus, which was accounted for in the analysis. The determined spectroscopic constants make it possible to build a list of very accurate rest-frequencies for astrophysical purposes in the THz region with 1σ uncertainties lower than 0.01 km s−1 in radial equivalent velocity
Accurate rest frequencies for the submillimetre-wave lines of C3O in ground and vibrationally excited states below 400 cm-1.
No full textThe submillimetre-wave spectrum of C3O () has been investigated in the laboratory using a source-modulation microwave spectrometer equipped with a gas-phase flow pyrolysis system for the production of unstable chemical species. C3O was produced by thermal decomposition of fumaryl chloride at 900 °C. Thirty-seven new rotational transitions were observed in the frequency range 307–740 GHz for the ground vibrational state, reaching a J quantum number as high as 76. Additionally, new millimetre-wave and submillimetre-wave lines were recorded for the bending fundamental , and for its overtones and whose rotational spectra have been identified for the first time.
The new laboratory measurements provide much improved rest frequencies in the submillimetre spectral region for the ground state spectra of C3O, and for the first levels of its low-energy v5 vibrational ladder, useful for the radioastronomical identification of their rotational lines in the ISM
Improved rest frequencies for the submillimetre-wave spectrum of SiN.
No full textThe submillimetre-wave spectrum of the SiN radical has been investigated in the laboratory
using a source-modulation microwave spectrometer equipped with a negative glow discharge
cell.
SiN was produced in a SiCl4/N2 discharge plasma.
Twenty-one new fine and hyperfine components up to were observed reaching
a frequency as high as 740 GHz.
The new laboratory measurements provide much improved rest frequencies in the submillimetre
spectral region useful for the identification of SiN lines in hot core sources and
circumstellar shells
Accurate rest-frequencies of ketenimine (CH2CNH) at submillimetre wavelength
Full text linkContext. Imine compounds are thought to have a role in the interstellar formation of complex organic species, including pre-biotic molecules. Ketenimine (CH2CNH) is one of the four imines discovered in space. It was identified in Sgr B2(N-LMH) through the detection of three rotational lines in absorption.
Aims. We present an extensive laboratory study of the ground-state rotational spectrum of CH2CNH at submillimetre wavelengths, aimed at obtaining accurate rest-frequencies for radio-astronomical searches.
Methods. The investigation was carried out using a source-modulation microwave spectrometer equipped with a cell that is coupled to a pyrolysis apparatus working at 1000 degrees. The spectrum was recorded in the frequency range 80-620 GHz with the detection of 150 transitions.
Results. The newly measured transition frequencies were analysed with previously available microwave and far-infrared data, yielding accurate rotational constants of CH2CNH, the complete sets of quartic and sextic centrifugal distortion constants, and three octic constants. Several transitions exhibit a hyperfine structure due to the quadrupole and spin-rotation couplings of the N-14 nucleus, which were accounted for in the analysis.
Conclusions. The determined spectroscopic constants allowed for the computation of a list of highly accurate rest-frequencies for astrophysical purposes in the submillimetre and THz region with 1 sigma uncertainties that are lower than 0.1 km s(-1) in radial equivalent velocity
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Nitrogen fractionation towards a pre-stellar core traces isotope-selective photodissociation
Full text linkContext. Isotopologue abundance ratios are important to understand the evolution of astrophysical objects and ultimately the origins of a planetary system such as our own. With nitrogen being a fundamental ingredient of pre-biotic material, understanding its chemistry and inheritance is of fundamental importance to understand the formation of the building blocks of life.
Aims. We aim to study the 14N/15N ratio in HCN, HNC, and CN across the prototypical pre-stellar core L1544. This study allows us to test the proposed fractionation mechanisms for nitrogen.
Methods. We present here single-dish observations of the ground state rotational transitions of the 13C and 15N isotopologues of HCN, HNC, and CN with the IRAM 30 m telescope. We analyse their column densities and compute the 14N/15N ratio map across the core for HCN. The 15N fractionation of CN and HNC is computed towards different offsets across L1544.
Results. The 15N-fractionation map of HCN towards a pre-stellar core is presented here for the first time. Our map shows a very clear decrease in the 14N/15N ratio towards the southern edge of L1544, where carbon chain molecules present a peak, strongly suggesting that isotope-selective photodissociation has a strong effect on the fractionation of nitrogen across pre-stellar cores. The 14N/15N ratio in CN measured towards four positions across the core also shows a decrease towards the south-east of the core, while HNC shows the opposite behaviour. We also measured the 12CN/13CN ratio towards four positions across the core.
Conclusions. The uneven illumination of the pre-stellar core L1544 provides clear evidence that 15N fractionation of HCN and CN is enhanced towards the region more exposed to the interstellar radiation field. Isotope-selective photodissociation of N2 is then a crucial process to understand 15N fractionation, as already found in protoplanetary disks. Therefore, the 15N fractionation in pre-stellar material is expected to change depending on the environment within which pre-stellar cores are embedded. The 12CN/13CN ratio also varies across the core, but its variation does not affect our conclusions as to the effect of the environment on the fractionation of nitrogen. Nevertheless, the interplay between the carbon and nitrogen fractionation across the core warrants follow-up studies
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