During the next decade a tremendous advance will take place in instrumentation for spectroscopy of the interstellar medium. Major new facilities (ALMA, SOFIA, APEX, LMT, Herschel and others) will be constructed and commissioned, so that the science opportu

8Phillips,Vastel:Futuremmandsubmminstrumentation

rstdiscoverywasfollowedbymanyotherstudieswhichcon rmedthepresenceofverylargeamountofdoublydeuterated

formaldehyde(D2CO)aswellasammonia(ND2H)(e.g.Roue etal.2000,Loinardetal.2001).Gasphasechemicalmodelsaccountrelativelywellfortheobservationsoftheabundancesofsinglydeuteratedmoleculesbutmaynotbeabletocompletelyreproducethelargedeuterationsobservedformultiplydeuteratedmolecules.Thelargedeuterationscouldalsobeaprod-uctofactivechemistryonthegrainsurfacesaspredictedbyTielens1983withtwoprocesses:

1.Deuterationduringthemantleformationphase;

2.Evaporationofthemantlesicesresultingfromtheheatingofthenewlyformedstar,withinjectionintothegasphaseofthedeuteratedspecies.Theyear2002appearstobethecornerstoneinthestudyofdeuterationprocesseswiththe rstdetectionofatriplydeuteratedmolecule,ND3.Untilnow,thepos-sibilityfordetectingtriplydeuteratedmoleculeswassoremotethattheirlineswereomittedinthespectroscopiccatalogsforastrophysics.Theground-staterotationaltran-sitionat309.91GHzofND3hasbeendetectedwiththeCSOtowardstheBarnard1cloud(Lisetal.2002,seeFigure8)andtheNGC1333IRAS4Aregion(VanderTaketal.2002),withabundanceratios[ND3]/[NH3]～10 3and[ND3/H2]～10 11.Theyconcludethatreac-tionsinthegas-phasearemorelikelytoproducethesehighdegreesofdeuteration,ratherthangrainsurfacechemistry.Howevertheycannottotallyruleoutthepos-sibilitythatsurfaceprocessesalsocontributetothefor-mationofND3(cfRodgers&Charnley2001).Moreover,therecentdiscoveryofdoubly-deuteratedmethanolto-wardsIRAS16293-2422(CHD2OH/CH3OH～0.2,Pariseetal.2002)cannotbeaccountedforgas-phasemodels.Themostpromisingrouteforsuchmethanoldeuterationseemstobebysurfacechemistry.RecentobservationsoftheextendedD2COemissiontowardsL1689N(Cecca-rellietal.2002)pointedoutthedi cultyinexplainingtheD2COabundance,eitherwithgasphasemodelsorwithgrainsurfacechemistry.Themanyroutestodeuter-ationarenotfullyunderstoodandmoreobservationsarenecessarytoelucidatethesesprocesses.Veryrecently,doublydeuteratedhydrogensul dehasbeendetectedbyVasteletal.(inpreparation)withtheCSOtowardstheBarnard1cloudandtheDCO+(3→2)emissionpeakofNGC1333IRAS4A.Figure9showsasanexamplethe rstdetectionofD2S(11,1→00,0)togetherwithHDS(10,1→00,0).

Figure8.Spectrumofthe309.91GHzND3linetowards

Barnard1observedattheCSO.Theredlinesshowthe tstothepositionandstrengthofthehyper necompo-nents.

Figure9.HDS(10,1→00,0)andD2S(11,1→00,0)detec-tionswiththeCSOtowardstheDCO+(3→2)emissionpeakofNGC1333IRAS4A(Vasteletal.,inprepara-tion).

4.3.DepletionofCO

Gasphasespeciesareexpectedtobedepletedatthecen-tersofcold,darkclouds,sincetheytendtosticktothedustgrains.Aseriesofrecentobservationshasshownthat,insomecases,theabundanceofmoleculeslikeCOdecreasestowardthecorecenterofcold,denseclouds(L1498:Willacyetal.1998;IC5146:Krameretal.1999,