188 research outputs found
Photodissociation of HCN and HNC isomers in the 7-10 eV energy range
13 pågs.; 11 figs.; 1 tab.The ultraviolet photoabsorption spectra of the HCN and HNC isomers have been simulated in the 7-10 eV photon energy range. For this purpose, the three-dimensional adiabatic potential energy surfaces of the 7 lowest electronic states, and the corresponding transition dipole moments, have been calculated, at multireference configuration interaction level. The spectra are calculated with a quantum wave packet method on these adiabatic potential energy surfaces. The spectra for the 3 lower excited states, the dissociative electronic states, correspond essentially to predissociation peaks, most of them through tunneling on the same adiabatic state. The 3 higher electronic states are bound, hereafter electronic bound states, and their spectra consist of delta lines, in the adiabatic approximation. The radiative lifetime towards the ground electronic states of these bound states has been calculated, being longer than 10 ns in all cases, much longer that the characteristic predissociation lifetimes. The spectra of HCN is compared with the available experimental and previous theoretical simulations, while in the case of HNC there are no previous studies to our knowledge. The spectrum for HNC is considerably more intense than that of HCN in the 7-10 eV photon energy range, which points to a higher photodissociation rate for HNC, compared to HCN, in astrophysical environments illuminated by ultraviolet radiation. ©2016 AIP Publishing LLCThe research leading to these results
has received funding from the European Research Council
(ERC Grant No. 610256: NANOCOSMOS) and the Spanish
Ministerio de EconomĂa y Competividad under Grant Nos.
CSD2009-00038, AYA2009-07304, AYA2012-32032, and
FIS2014-52172-C2.Peer Reviewe
Estudio de la QuĂmica en la Envoltura Circunestelar IRC+10216
Tesis doctoral inĂ©dita. Universidad AutĂłnoma de Madrid, Facultad de Ciencias, Departamento de FĂsica TeĂłrica . Fecha de lectura: 28-06-200
Discovery of five cyano derivatives of propene with the QUIJOTE line survey
We report the discovery of five cyano derivatives of propene towards TMC-1
with the QUIJOTE line survey: and -crotononitrile
(-CHCHCHCN, -CHCHCHCN), methacrylonitrile (CHC(CH)CN),
and and -allyl cyanide (-CHCHCHCN and
-CHCHCHCN). The observed transitions allowed us to derive a common
rotational temperature of 71 K for all them. The derived column densities
are N(-CHCHCHCN)=(50.5)10 cm,
N(-CHCHCHCN)=(1.30.2)10 cm,
N(CHC(CH)CN)=(1.00.1)10 cm,
N(-CHCHCHCN)=(8.00.8)10 cm, and
N(-CHCHCHCN)=(7.00.7)10 cm, respectively.
The abundance of cyano-propene relative to that of propene is thus
10, which is considerably lower than those of other cyano
derivatives of abundant hydrocarbons. Upper limits are obtained for two ethynyl
derivatives of propene ( and -CHCHCHCCH).Comment: Accepted for publication in Astronomy and Astrophysics Letter
Discovery of Interstellar Propylene (CH_2CHCH_3): Missing Links in Interstellar Gas-Phase Chemistry
We report the discovery of propylene (also called propene, CH_2CHCH_3) with
the IRAM 30-m radio telescope toward the dark cloud TMC-1. Propylene is the
most saturated hydrocarbon ever detected in space through radio astronomical
techniques. In spite of its weak dipole moment, 6 doublets (A and E species)
plus another line from the A species have been observed with main beam
temperatures above 20 mK. The derived total column density of propylene is 4
10^13 cm^-2, which corresponds to an abundance relative to H_2 of 4 10^-9,
i.e., comparable to that of other well known and abundant hydrocarbons in this
cloud, such as c-C_3H_2. Although this isomer of C_3H_6 could play an important
role in interstellar chemistry, it has been ignored by previous chemical models
of dark clouds as there seems to be no obvious formation pathway in gas phase.
The discovery of this species in a dark cloud indicates that a thorough
analysis of the completeness of gas phase chemistry has to be done.Comment: 13 pages, 2 figures, accepted for publication in ApJ
Discovery of two new interstellar molecules with QUIJOTE: HCCCHCCC and HCCCCS
We report on the discovery of two new molecules, HCCCHCCC and HCCCCS, towards
the starless core TMC-1 in the Taurus region from the QUIJOTE line survey in
the 31.1-50.2 GHz frequency range. We identify a total of twenty-nine lines of
HCCCHCCC and six rotational transitions of HCCCCS. The rotational quantum
numbers range from Ju=10 up to 15 and Ka <=2 for HCCCHCCC and Ju=21/2 up to
31/2 for HCCCCS. We derived a column density for HCCCHCCC of
N=(1.3+/-0.2)x10^11 cm-2 with a rotational temperature of 6+/-1 K, while for
HCCCCS we derived N=(9.5+/-0.8)x10^10 cm-2 and Trot =10+/-1 K. The abundance of
HCCCHCCC is higher than that of its recently discovered isomer, l-H2C6. If we
compare HCCCCS with its related molecules, HCS and HCCS, we obtain abundance
ratios HCS/HCCCCS=58 and HCCS/HCCCCS=7.2. We investigated the formation of
these two molecules using chemical modelling calculations. The observed
abundances can be accounted for by assuming standard gas-phase formation routes
involving neutral-neutral reactions and ion-neutral reactions.Comment: arXiv admin note: text overlap with arXiv:2206.0899
Detection of C3O in IRC+10216: Oxygen-Carbon chain chemistry in the outer envelope
The oxygen-bearing species C3O has been identified in the circumstellar envelope of the carbon star IRC +10216. The J = 8-->7, 9-->8, 10-->9, 14-->13, and 15-->14 transitions were detected at 2 and 3 mm using the Arizona Radio Observatoryâs 12 m telescope. Measurements of the J = 9-->8, 10-->9, and 12-->11 lines were simultaneously conducted at the IRAM 30 m telescope. The line profiles of C3O are roughly U-shaped, indicating an extended shell distribution for this molecule in IRC +10216. The total column density derived for C3O is 1.2x10^12 cm^-2, at least an order of magnitude higher than that predicted by current chemical models. However, a revised model that includes reactions of atomic oxygen with carbon-chain radicals, such as l-C3H and C4, can reproduce the observed abundance. This model also predicts that C3O arises from a shell source with an outer radius near
r ⌠30", consistent with the observations. These results suggest that gas phase neutral-neutral chemistry may be
producing the oxygen-bearing molecules present in the outer envelope of IRC +10216.This material is based on work supported by the National Aeronautics and Space Administration through the NASA Astrobiology
Institute under Cooperative Agreement CAN-02-OSS-02 issued through the Office of Space Science. We also acknowledge support from Spanish MEC under project AYA2003-2785 and from "Comunidad de Madrid" under
PRICIT project S-0505/ESP-0237 (ASTROCAM). E. D. T. thanks NSF for a graduate research fellowship, and M. A. acknowledges Spanish MEC for a predoctoral grant AP2003-4619.Peer reviewe
The magnesium paradigm in IRC+10216: Discovery of MgCH, MgCN, MgCH, and MgCN
We found four series of harmonically related lines in IRC\,+10216 with the
Yebes\,40m and IRAM\,30m telescopes. The first series corresponds to a molecule
with a rotational constant, , of 1448.59940.0013 MHz and a distortion
constant, , of 63.451.15 Hz and covers upper quantum numbers from
=11 up to 33 (B1449). The second series is fitted with
=1446.93800.0098 MHz and =9123 Hz and covers upper quantum
numbers from =11 up to 17 (B1447). The third series is fitted with
=598.74950.0011 MHz and D=6.130.43 Hz and covers quantum numbers
from =26 up to 41 (B599). Finally, the frequencies of the last series of
lines can be reproduced with =594.31760.0026 MHz and =4.921.16
Hz (B594). The large values of point toward four metal-bearing carriers.
After exploring all plausible candidates containing Na, Al, Mg, and other
metals, our ab initio calculations indicate that the cations MgCH,
MgCN, MgCH, and MgCN must be the carriers of B1449,
B1447, B599, and B594, respectively. These cations could be formed by the
radiative association of Mg with CH, CN, CH, and CN,
respectively. We calculated the radiative association rate coefficient of
Mg with CH, CN, CH, and CN and incorporated them in our
chemical model. The results confirm that the Mg-bearing cations can be formed
through these radiative association reactions in the outer layers of
IRC\,+10216. This is the first time that cationic metal-bearing species have
been found in space. These results provide a new paradigm on the reactivity of
ionized metals with abundant radicals and open the door for further
characterization of similar species in metal-rich astrophysical environments
Astronomical identification of CN-, the smallest observed molecular anion
We present the first astronomical detection of a diatomic negative ion, the
cyanide anion CN-, as well as quantum mechanical calculations of the excitation
of this anion through collisions with para-H2. CN- is identified through the
observation of the J = 2-1 and J = 3-2 rotational transitions in the C-star
envelope IRC +10216 with the IRAM 30-m telescope. The U-shaped line profiles
indicate that CN-, like the large anion C6H-, is formed in the outer regions of
the envelope. Chemical and excitation model calculations suggest that this
species forms from the reaction of large carbon anions with N atoms, rather
than from the radiative attachment of an electron to CN, as is the case for
large molecular anions. The unexpectedly large abundance derived for CN-, 0.25
% relative to CN, makes likely its detection in other astronomical sources. A
parallel search for the small anion C2H- remains so far unconclusive, despite
the previous tentative identification of the J = 1-0 rotational transition. The
abundance of C2H- in IRC +10216 is found to be vanishingly small, < 0.0014 %
relative to C2H.Comment: 5 pages, 4 figures; accepted for publication in A&A Letter
Laboratory and astronomical discovery of the cyanovinyl radical H2CCCN
We report the first laboratory and interstellar detection of the alpha-cyano
vinyl radical (H2CCCN). This species was produced in the laboratory by an
electric discharge of a gas mixture of vinyl cyanide, CH2CHCN, and Ne, and its
rotational spectrum was characterized using a Balle-Flygare narrowband-type
Fourier-transform microwave spectrometer operating in the frequency region of
8-40 GHz. The observed spectrum shows a complex structure due to tunneling
splittings between two torsional sublevels of the ground vibronic state, 0+ and
0-, derived from a large-amplitude inversion motion. In addition, the presence
of two equivalent hydrogen nuclei makes necessary to discern between ortho- and
para-H2CCCN. A least squares analysis reproduces the observed transition
frequencies with a standard deviation of ca. 3 kHz. Using the laboratory
predictions, this radical is detected in the cold dark cloud TMC-1 using the
Yebes 40m telescope and the QUIJOTE line survey. The 404-303 and 505-404
rotational transitions, composed of several hyperfine components, were observed
in the 31.0-50.4 GHz range. Adopting a rotational temperature of 6K we derive a
column density of (1.4+/-0.2)e11 cm-2 and (1.1+/-0.2)e11 cm-2 for ortho-H2CCCN
and para-H2CCCN, respectively. The reactions C + CH3CN, and perhaps also N +
CH2CCH, emerge as the most likely routes to H2CCCN in TMC-1.Comment: Accepted for publication in A&A Letters on 18/07/202
Ultra-deep 31.0-50.3 GHz spectral survey of IRC+10216
51 pags., 43 figs., 3 tabs.Context. The carbon-rich envelope of the asymptotic giant branch star CW Leo, IRC+10216, is one of the richest molecular sources in the sky. Available spectral surveys below 51 GHz are more than 25 years old, and new work is needed. Aims. Characterizing the rich molecular content of this source, specially for heavy species, requires carrying out very sensitive spectral surveys at low frequencies. In particular, we have achieved an rms in the range 0.2-0.6mK per MHz. Methods. Long Q band (31.0-50.3 GHz) single-dish integrations were carried out with the Yebes-40m telescope using specifically built receivers. The most recent line catalogs were used to identify the lines. Results. The data contain 652 spectral features, corresponding to 713 transitions from 81 species (we count the isomers, isotopologs, and ortho/para species separately). Only 57 unidentified lines remain with signal-to-noise ratios â€3. Some new species and/or vibrational modes have been discovered for the first time with this survey. Conclusions. This IRC+10216 spectral survey is by far the most sensitive survey carried out to date in the Q band. It therefore provides the most complete view of IRC+10216 from 31.0 to 50.3 GHz, giving unique information about its molecular content, especially for heavy species. Rotational diagrams built from the data provide valuable information about the physical conditions and chemical content of this circumstellar envelope.We thank Ministerio de Ciencia e InnovaciĂłn of Spain
for funding support through projects PID2019-106110GB-I00, PID2019-
107115GB-C21/AEI/10.13039/501100011033, PID2019-106235GB-I00, and
grant FJCI-2016-27983 for CB. We also thank ERC for funding through grant
ERC-2013-Syg-610256-NANOCOSMOS. M.A. thanks MICIU for grant RyC2014-16277
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