192 research outputs found
Modelling line emission of deuterated H_3^+ from prestellar cores
Context: The depletion of heavy elements in cold cores of interstellar
molecular clouds can lead to a situation where deuterated forms of H_3^+ are
the most useful spectroscopic probes of the physical conditions.
Aims: The aim is to predict the observability of the rotational lines of
H_2D^+ and D_2H^+ from prestellar cores.
Methods: Recently derived rate coefficients for the H_3^+ + H_2 isotopic
system were applied to the "complete depletion" reaction scheme to calculate
abundance profiles in hydrostatic core models. The ground-state lines of
H_2D^+(o) (372 GHz) and D_2H^+(p) (692 GHz) arising from these cores were
simulated. The excitation of the rotational levels of these molecules was
approximated by using the state-to-state coefficients for collisions with H_2.
We also predicted line profiles from cores with a power-law density
distribution advocated in some previous studies.
Results: The new rate coefficients introduce some changes to the complete
depletion model, but do not alter the general tendencies. One of the
modifications with respect to the previous results is the increase of the D_3^+
abundance at the cost of other isotopologues. Furthermore, the present model
predicts a lower H_2D^+ (o/p) ratio, and a slightly higher D_2H^+ (p/o) ratio
in very cold, dense cores, as compared with previous modelling results. These
nuclear spin ratios affect the detectability of the submm lines of H_2D^+(o)
and D_2H^+(p). The previously detected H_2D^+ and D_2H^+ lines towards the core
I16293E, and the H_2D^+ line observed towards Oph D can be reproduced using the
present excitation model and the physical models suggested in the original
papers.Comment: 10 pages, 11 Figures; ver2: updated some of the Figures, added some
references, added an entry to acknowledgement
Vibrational and rotational spectroscopy of CD2H+
The lowest rotational levels (=0-5) of the CDH
ground state have been probed by high-resolution
rovibrational and pure rotational spectroscopy
in a cryogenic 22-pole ion trap.
For this, the rovibrational band has been
revisited\footnote{M.-F. Jagod et al, J. Molec. Spectrosc. 153, 666, 1992},
detecting 107 transitions, among which 35 are new. The use of a frequency comb system allowed to measure
the rovibrational transitions with high precision and accuracy, typically better than 1~MHz.
The high precision has been confirmed by comparing
combination differences in the ground and vibrationally excited state.
For the ground state, this allowed for equally precise
predictions of pure rotational transitions, 24 of which have
been measured directly by a novel IR - mm-wave
double resonance
method\footnote{S. G\"artner et al, J. Phys. Chem. A 117, 9975, 2013}
How can a 22-pole ion trap exhibit 10 local minima in the effective potential?
The column density distribution of trapped OH ions in a 22-pole ion trap
is measured for different trap parameters. The density is obtained from
position-dependent photodetachment rate measurements. Overall, agreement is
found with the effective potential of an ideal 22-pole. However, in addition we
observe 10 distinct minima in the trapping potential, which indicate a breaking
of the 22-fold symmetry. Numerical simulations show that a displacement of a
subset of the radiofrequency electrodes can serve as an explanation for this
symmetry breaking
Evidence for Multiple Pathways to Deuterium Enhancements in Protoplanetary Disks
The distributions of deuterated molecules in protoplanetary disks are
expected to depend on the molecular formation pathways. We use observations of
spatially resolved DCN emission from the disk around TW Hya, acquired during
ALMA Science verification with a ~3" synthesized beam, together with comparable
DCO+ observations from the Submillimeter Array, to investigate differences in
the radial distributions of these species and hence differences in their
formation chemistry. In contrast to DCO+, which shows an increasing column
density with radius, DCN is better fit by a model that is centrally peaked. We
infer that DCN forms at a smaller radii and thus at higher temperatures than
DCO+. This is consistent with chemical network model predictions of DCO+
formation from H2D+ at T<30 K and DCN formation from additional pathways
involving CH2D+ at higher temperatures. We estimate a DCN/HCN abundance ratio
of ~0.017, similar to the DCO+/HCO+ abundance ratio. Deuterium fractionation
appears to be efficient at a range of temperatures in this protoplanetary disk.
These results suggest caution in interpreting the range of deuterium fractions
observed in Solar System bodies, as multiple formation pathways should be taken
into account.Comment: accepted for publication in Ap
Formation of Nitriles in the Interstellar Medium via Reactions of Cyano Radicals, CN(X 2Σ+), with Unsaturated Hydrocarbons
Crossed molecular beam experiments of cyano radicals, CN(X 2Σ+, ν = 0), in their electronic and vibrational ground state reacting with unsaturated hydrocarbons acetylene, C2H2(X 1Σ), ethylene, C2H4(X 1Ag), methylacetylene, CH3CCH(X 1A1), allene, H2CCCH2(X 1A1), dimethylacetylene, CH3CCCH3(X 1A1'), and benzene, C6H6 (X 1A1g), were performed at relative collision energies between 13.3 and 36.4 kJ mol-1 to unravel the formation of unsaturated nitriles in the outflows of late-type AGB carbon stars and molecular clouds. In all reactions, the CN radical was found to attack the π electron density of the hydrocarbon molecule with the radical center located at the carbon atom; the formation of an initial addition complex is a prevalent pathway on all the involved potential energy surfaces. A subsequent carbon-hydrogen bond rupture yields the nitriles cyanoacetylene, HCCCN (X 1Σ+), vinylcyanide, C2H3CN (X 1A'), 1-methylcyanoacetylene, CH3CCCN (X 1A1), cyanoallene, H2CCCH(CN) (X 1A'), 3-methylcyanoacetylene, HCCCH2CN(X 1A'), 1,1-cyanomethylallene, H2CCC(CN)(CH3) (X 1A'), and cyanobenzene, C6H5CN (X 1A1). In case of acetylene and ethylene, a second reaction channel involves a [1, 2]-H atom shift in the initial HCCHCN and H2CCH2CN collision complexes prior to a hydrogen atom release to form cyanoacetylene, HCCCN (X 1Σ+), and vinylcyanide, C2H3CN (X 1A'). Since all these radical-neutral reactions show no entrance barriers, have exit barriers well below the energy of the reactant molecules, and are exothermic, the explicit identification of this CN versus H atom exchange pathway under single collision conditions makes this reaction class a compelling candidate to synthesize unsaturated nitriles in interstellar environments holding temperatures as low as 10 K. This general concept makes it even feasible to predict the formation of nitriles once the corresponding unsaturated hydrocarbons are identified in the interstellar medium. Here HCCCN, C2H3CN, and CH3CCCN have been already observed; since CH3CCH is the common precursor to H2CCCH(CN)/CH3CCCN and the latter isomer has been assigned unambiguously toward TMC-1 and OMC-1, H2CCCH(CN) is strongly expected to be present in both clouds as well. The formation of isonitrile isomers was not observed in our experiments. Since all reactions to HCCNC, C2H3NC, CH3CCNC, H2CCCH(NC), H2CCC(NC)(CH3), and C6H5NC are either endothermic or the exit barrier is well above the energy of the reactants, neutral-neutral reactions of cyano radicals with closed shell unsaturated hydrocarbons cannot synthesize isonitriles in cold molecular clouds. However, in outflow of carbon stars, the enhanced translational energy of both reactants close to the photosphere of the central star can compensate this endothermicity, and isonitriles might be formed in these hotter environments as well
Efectos de un programa de fortalecimiento físico en la condición funcional de adultos mayores
A sedentary lifestyle is becoming a constant threat to public health, since it represents one of the main causes of disease (Pedraza, 2019), which suggests promoting preventive measures to avoid dependence for the realization of ABVD. Objective: to improve the level of independence of older adults by implementing a physical strengthening program to reduce sedentary lifestyle in a Day House in Toluca. Methodology: quantitative study of quasi-experimental, descriptive and cross-sectional type with a non-probabilistic sample of 70 older adults with the following inclusion criteria: being 60 years and older, being enrolled in the Day House of Toluca, presenting a sedentary lifestyle and signing prior informed consent, the exclusion criteria considered: dependent older adults or with the presence of any disease that prevents the performance of physical activity, diagnosis of neurocognitive disorder or use of geriatric assistants. Instrument: Senior Fitness Test (SFT) with reliability index of 0.9 that evaluates muscle strength, aerobic endurance, flexibility and agility through an interval scale classified by age and gender. Results: The physical strengthening program improved the level of independence for the performance of ABVD of 41% of older adults participating.El sedentarismo se está convirtiendo en una amenaza constante para la salud pública, toda vez que representa una de las principales causas de enfermedad (Pedraza, 2019) lo que sugiere promover medidas preventivas para evitar dependencia para la realización de ABVD. Objetivo: mejorar la condición funcional de adultos mayores mediante la implementación de un programa de fortalecimiento físico para disminuir el sedentarismo en una Casa de Día de Toluca. Metodología: estudio cuantitativo de tipo cuasi experimental, descriptivo y transversal con una muestra no probabilística de 70 adultos mayores con los siguientes criterios de inclusión: tener de 60 años en adelante, estar inscrito en la Casa de Día de Toluca, presentar sedentarismo y firmar previo consentimiento informado, los criterios de exclusión considerados: adultos mayores dependientes o con presencia de alguna enfermedad que impida la realización de actividad física, diagnóstico de trastorno neurocognitivo o uso de auxiliares geriátricos. Instrumento: Senior Fitness Test (SFT) con índice de confiabilidad de 0.9 que evalúa fuerza muscular, resistencia aeróbica, flexibilidad y agilidad a través de una escala de intervalo clasificada por edad y género. Resultados: El programa de fortalecimiento físico mejoró el nivel de condición funcional del 41% de adultos mayores participantes
Detection of Interstellar Ortho-D2H+ with SOFIA
We report on the detection of the ground-state rotational line of ortho-D2H+ at 1.477 THz (203 mu m) using the German REceiver for Astronomy at Terahertz frequencies (GREAT) on. board the Stratospheric Observatory For Infrared Astronomy (SOFIA). The line is seen in absorption against. far-infrared continuum from the protostellar binary IRAS 16293-2422 in Ophiuchus. The para-D2H+ line at 691.7 GHz was not detected with the APEX telescope toward this position. These D2H+ observations complement our previous detections of para-H2D+ and ortho-H2D+ using SOFIA and APEX. By modeling chemistry and radiative transfer in the dense core surrounding the protostars, we find that the ortho-D2H+ and para-H2D+ absorption features mainly originate in the cool (T <18 K) outer envelope of the core. In contrast, the ortho-H2D+ emission from the core is significantly absorbed by the ambient molecular cloud. Analyses of the combined D2H+ and H2D+ data result in an age estimate of similar to 5. x. 10(5) yr for the core, with an uncertainty of similar to 2. x. 10(5) yr. The core material has probably been pre-processed for another 5. x. 10(5) years in conditions corresponding to those in the ambient molecular cloud. The inferred timescale is more than 10 times the age of the embedded protobinary. The D2H+ and H2D+ ions have large and nearly equal total (ortho+ para) fractional abundances of similar to 10(-9) in the outer envelope. This confirms the central role of H-3 + in the deuterium chemistry in cool, dense gas, and adds support to the prediction of chemistry models that also D-3(+) should be abundant in these conditions.Peer reviewe
A computed line list for the H2D+ molecular ion
A comprehensive, calculated line list of frequencies and transition
probabilities for the singly deuterated isotopologue of H3+, H2D+, is
presented. The line list, called ST1, contains over 22 million
rotational-vibrational transitions occurring between more than 33 thousand
energy levels; it covers frequencies up to 18500 cm-1. All energy levels with
rotational quantum number, J, up to 20 are considered, making the line list
useful for temperatures up to at least 3000 K. About 15% of these levels are
fully assigned with approximate rotational and vibrational quantum numbers. The
list is calculated using a previously proposed, high accuracy, ab initio model
and consistency checks are carried out to test and validate the results. These
checks confirm the accuracy of the list. A temperature-dependent partition
function, valid over a more extended temperature range than those previously
published, and cooling function are presented. Temperature-dependent synthetic
spectra in the frequency range 0 - 10000 cm-1 are also given.Comment: 7 pages, 3 figures, 5 table
Vibrational spectroscopy of H2He+ and D2He+
Contains fulltext :
233355 .pdf (Publisher’s version ) (Closed access
Deuterated formaldehyde in rho Ophiuchi A
From mapping observations of H2CO, HDCO, and D2CO, we have determined how the
degree of deuterium fractionation changes over the central 3'x3' region of rho
Oph A. The multi-transition data of the various H2CO isotopologues, as well as
from other molecules (e.g., CH3OH and N2D+) present in the observed bands, were
analysed using both the standard type rotation diagram analysis and, in
selected cases, a more elaborate method of solving the radiative transfer for
optically thick emission. In addition to molecular column densities, the
analysis also estimates the kinetic temperature and H2 density. Toward the SM1
core in rho Oph A, the H2CO deuterium fractionation is very high. In fact, the
observed D2CO/HDCO ratio is 1.34+/-0.19, while the HDCO/H2CO ratio is
0.107+/-0.015. This is the first time, to our knowledge, that the D2CO/HDCO
abundance ratio is observed to be greater than 1. The kinetic temperature is in
the range 20-30 K in the cores of rho Oph A, and the H2 density is (6-10)x10^5
cm-3. We estimate that the total H2 column density toward the deuterium peak is
(1-4)x10^23 cm-2. As depleted gas-phase chemistry is not adequate, we suggest
that grain chemistry, possibly due to abstraction and exchange reactions along
the reaction chain H2CO -> HDCO -> D2CO, is at work to produce the very high
deuterium levels observed.Comment: 17 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
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