The Chemistry in Interstellar Clouds Eric Herbst Departments of Physics, Astronomy, and Chemistry The Ohio State University

Andromeda: a “nearby” spiral galaxy 100,000 lt yr

Molecules seen at long wavelengths 10 K 10(4) cm-3 H2 dominant sites of star formation Cold Dense Interstellar Cloud Dust particles block out light

Dust constitutes 1% of mass in a cloud. IR spectral studies yield information about molecules in the gas and on dust particles but the technique is difficult.

+ small grains and PAH’s Water, CO, CO2 Studied by infrared spectroscopy

The Eagle Nebula: active star forming region in our galaxy

The Horsehead Nebula (also in our galaxy)

Radio astronomy to study gaseous molecules

LMT (Large Millimeter Wave Telescope)

MOLECULAR ROTATION “radio” emissions  E = h Unlike vibrations, rotations occur only in the gas.

The Case of TMC-1 CO J=1  0

133 neutral molecules (September 2008) 18 molecular ions 14 positive 4 negative H C, N, O S, Si, P, K, Na, Mg, Al, F 2-13 atoms Spectra tell us what molecules are there, what concentrations they have, and what the physical conditions are. Gaseous Interstellar Molecules

Exotic Molecules Molecular ions – positive and negative – HCO + C 4 H - Free radicals – odd number of electrons – C 2 H Isomers – unusual structures HNC Three-membered rings of carbon atoms Hydrogen-poor molecules BUT STILL MAINLY ORGANIC!!!!!

Gaseous interstellar molecules (>150) N=2 N=3N=4 N = 5N = 6N = 7N = 8N = 9N = 10 H2H2 AlClCH 2 C2SC2SNH 3 CH 4 CH 3 OHCH 3 NH 2 HCOOCH 3 (CH 3 ) 2 O(CH 3 ) 2 CO CHPNH2SH2SOCSH 2 COSiH 4 CH 3 SHCH 3 CCHCH 3 C 2 CNC 2 H 5 OHCH 3 C 4 CN NHSiNNH 2 CCPH 2 CSCH 2 NHC2H4C2H4 CH 3 CHOHC 6 HC 2 H 5 CNCH 3 CH 2 CHO OHSiOH2OH2OSiNCH 2 CNC5C5 H2C4H2C4 c-CH 2 OCH 2 C7HC7HCH 3 C 4 H(CH 2 OH) 2 O 2 (?)SiSHNONaCNl-C 3 Hl-C 3 H 2 CH 3 CNCH 2 CHCN HOCH 2 CHO C8HC8H HFPOC2HC2HSO 2 c-C 3 Hc-C 3 H 2 CH 3 NCHC 4 CNCH 3 COOHHC 6 CN C2C2 SHHCNN2ON2OHCCHH 2 CCNNH 2 CHOC6HC6H H 2 CCCHCN CH 3 CONH 2 N = 11 CNAlFHNCSiCNHNCOH 2 NCNCH 2 CNHH 2 CCHOHH2C6H2C6 CH 2 CHCH 3 HC 8 CN COFeOHCOHNCSCH 2 COC5HC5H CH 2 CHCHO CH 3 C 6 H CSSiCc-SiC 2 HCCNHCOOHC5NC5NC2H6C2H6 CPMgCN C 2 CNC4HC4HHC 4 NNH 2 CH 2 CN NO MgNCC3OC3OHC 2 CNC 5 S(?) N = 12 NS AlNC H 3 + C3SC3SHC 2 NCHC 4 H C6H6C6H6 SO HCP HCO + c-SiC 3 C 4 Si HCl CH + C3C3 HOC + C3N-C3N- HNCCCHC 2 CHO NaCl CO + C2OC2O N2H+N2H+ H3O+H3O+ CNCHOc-C 3 H 2 O N = 13 KCl SO + CO 2 HCS + HCNH + H 2 COH + HC 10 CN N 2 (?) CF + HCNOHOCO + C4H-C4H- HC 3 NH + C6H-C6H- C8H-C8H-

The Chemistry in Cold Interstellar Clouds Why is it so unusual? Atoms  Molecules in the gas and on dust particles

Chemical Reactions The higher the temperature, the faster the reaction. Activation energy

In Cold Interstellar Clouds Must be all downhill at low temperatures!

Cosmic rays produce ions

FORMATION OF GASEOUS WATER H 2 + COSMIC RAYS  H e Elemental abundances: C,O,N = 10(-4); C<O H H 2  H H H O  OH + + H 2 OH n + + H 2  OH n H H 3 O + + e  H 2 O + H; OH + 2H, etc

Solved kinetically; yields concentrations of all molecules as a function of time in clouds. Best agreement with cold cloud gas at 10(5) – 10(6) yr; 80% of molecules reproduced. Predicts new molecules.

TYPES OF SURFACE REACTIONS REACTANTS: MAINLY MOBILE ATOMS AND RADICALS A + B  AB association H + H  H 2 H + X  XH (X = O, C, N, CO, etc.) WHICH CONVERTS O  OH  H 2 O C  CH  CH 2  CH 3  CH 4 N  NH  NH 2  NH 3 CO  HCO  H 2 CO  H 3 CO  CH 3 OH

Formation of Ices In Cold Cores H O OH H H2OH2O Other ices formed: methane, ammonia, CO, CO2, formaldehyde, methanol (all confirmed by experiments at low temperature.)

Gas-Grain Models In cold cores, ice mantles build up as chemistry proceeds both in the gas and on surfaces. In hotter regions, grain mantles are released into the gas and change the chemistry to a saturated one.

Cold Core Protostar Star + Disk T = 10 Kn = 10 4 cm -3 adiabatic collapse hot core 100 K Low-mass Star Formation Molecule factory

SOME ORGANIC MOLECULES IN LATEST HOT CORE MODEL Dimethyl ether, methyl formate, formic acid, glycolaldehyde, acetic acid, ethanol, acetaldehyde, ketene, acetone, ethylene glycol Methyl amine, urea, formamide, acetamide, methoxyamine, hydroxymethylamine Garrod, Widicus Weaver, & Herbst (2008)

The Future Other New Telescopes

The soon-to-be Herschel Space Observatory

ALMA: the future…….

A starburst galaxy……