Future MmSubmm Instrumentation and Science Opportunities Exa(5)

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

Phillips,Vastel:Futuremmandsubmminstrumentation

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Figure6.WatertransitionsavailabletoHIFI.Bands1-5coversthefrequencyrange472-1280Gz;Band6covers1400-1904GHz;Gap5-6isthefrequencyrangebetweenBand5andBand6,whichmaynotbecovered.ground”speciesarelight,fastrotators,typi edbythedi-atomichydrides.Someofthese,e.g.NaH,CaH,MgH,...havebeensearchedforinJ=0→1transitionsusingatmosphericwindowsforground-basedtelescopes,withnegativeresults,butcanbesearchedfornow,within-creasedsensitivity,intwoways.The rstmethod(canbecarriedoutfromthegroundinfavorablecases)makesuseofcoldcloudsonthelineofsighttopowerfulcontinuumsources,suchasSgrB2.There,inthecolddarkclouds,themoleculeswillbeinthegroundstateandwouldbede-tectedinabsorption.ThismethodavoidstheconfusioninthespectraofGMCs,sincethelineforestislargelymadeupofhighlyexcitedmolecularlines,which,ofcourse,isnotthecaseforthehydridesincoldclouds.Agoodex-ampleisseenintheSWASdetectionoftheground-stateH2OlineinSgrB2(Figure4).Thesecondmethoddoessu erfromGMClineconfusion,butmakesuseofthenewhighfrequencycapabilitiesforHIFIandSOFIA,wherethehighJlinesofthevarioushydrideswillhavemuchhigherlinestrengthsthan1→0;hopefullythiswillover-cometheline-foreste ectinthehightemperatureand

highdensitysources.

Generally,above1THzthealmostzeroatmospherictrans-missionhaspreventedstudiessofar,butseveralwindowsoflimitedsizeandstrengthhavebeenrecentlydetectedonhighsites.SpaceplatformswillallowstudiesofHD(1→0)at2.67THz,HeH+(1→0)at2.01THz,N+at1.46and2.46THz,HFat1.23THz,FeHat1.41THz,OHat1.83THz,OH+at2.46THz,etc...SomespecieshavebeendetectedbyISO,e.g.CH+inthehighJtran-sitions(Cernicharoetal.1997),HF(Neufeldetal.1997)andHD(Wrightetal.1999,Cauxetal.2002).HIFIwillbeagreatimprovementcomparedtowhatusedtobeavailableonISO.

4.Deuterium

Oneofthemostimportantaspectsofmolecularspec-troscopyoftheinterstellarmediumisthestudyoftheabundanceofdeuterium.Thenewfacilitieswillprovideamuchwiderrangeoffrequenciesandsensitivities,sothatthedeuteriumstudiescanbeextendedtonewspeciesandnewobjects.Thefundamentalaspectofdeuterium