J/A+A/675/A69ivo://CDS.VizieR/J/A+A/675/A69doi:10.26093/cds/vizier.36750069CDSJacob A.M.Menten K.M.Wyrowski F.Sipila O.2024-11-28T20:04:26Z2023-07-04T08:41:13ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frmolecular-cloudsinfrared-sourcesspectroscopyWhile the abundance of elemental deuterium is relatively low (D/H ~ a few x 10^-5^), orders of magnitude higher D/H abundance ratios have been found for many interstellar molecules, enhanced by deuterium fractionation. In cold molecular clouds (T<20K) deuterium fractionation is driven by the H_2_D^+^ ion, whereas at higher temperatures (T>20-30K) gas-phase deuteration is controlled by reactions with CH_2_D^+^ and C_2_HD^+^. While the role of H_2_D^+^ in driving cold interstellar deuterium chemistry is well understood, thanks to observational constraints from direct measurements of H_2_D^+^, deuteration stemming from CH_2_D^+^ is far less understood, as a result of the absence of direct observational constraints of its key ions. Therefore, making use of chemical surrogates is imperative in order to explore deuterium chemistry at intermediate temperatures. Formed at an early stage of ion-molecule chemistry directly from the dissociative recombination of CH_3_^+^ (CH_2_D^+^), CH (CD) is an ideal tracer for investigating deuterium substitution initiated by reactions with CH_2_D^+^. This paper reports the first detection of CD in the interstellar medium (ISM), carried out using the APEX 12m telescope towards the widely studied low-mass protostellar system IRAS 16293-2422. Observed in absorption toward the envelope of the central protostar, the D/H ratio derived from the column densities of CD and CH is found to be 0.016+/-0.003. This is an order of magnitude lower than the values found for %that derived using other small molecules like C_2_H and H_2_CO observed in emission but whose formation, which is similar to that of CH, is also initiated via pathways involving warm deuterium chemistry. Gas-phase chemical models reproducing the CD/CH abundance ratio suggest that it reflects 'warm deuterium chemistry' (which ensues in moderately warm conditions of the ISM) and illustrates the potential use of the CD/CH ratio in constraining the gas temperatures of the envelope gas clouds it probes.2023A&A...675A..69Jhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/675/A69CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/675/A69https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/675/A69http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/675/A69https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/675/A69https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/675/A69http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/675/A69GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/675/A69/list (List of fits spectra)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/675/A69/list?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/675/A69/list?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/675/A69/list?GETtext/xml+votable180.050000true248.09489-24.477440.0055555555555555566/42970https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/675/A69?format=asciiInfrareddefaultJ/A+A/675/A69/listList of fits spectraspShow the spectrummeta.ref.urlcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right Ascension of center (J2000)degpos.eq.ra;meta.mainDEJ2000Declination of center (J2000)degpos.eq.dec;meta.mainNxNumber of pixels along X-axismeta.numberintObs.dateObservation datestime.epoch;obsnullablebFreqLower value of frequency intervalHzem.freq;stat.mindoubleBFreqUpper value of frequency intervalHzem.freq;stat.maxdoubledFreqFrequency resolutionHzspect.resolutionintvlsrSource LSR velocitykm/sphys.veloc;pos.lsrfloatTcMain-beam brightness continuum temperature at 440GHzKphys.temperature;spect.continuumfloatParityParity of the N=1, J=3/2-1/2 transitions of CDphys.atmol.paritycharsizeSize of FITS fileKibytephys.size;meta.fitsintFileNameName of FITS file, in subdirectory fitsmeta.id;meta.fitscharTitleTitle of the FITS filemeta.title;meta.fitschar