Molecules: Probes of the Interstellar Medium ERIC HERBST DEPARTMENTS OF PHYSICS, CHEMISTRY, AND ASTRONOMY THE OHIO STATE UNIVERSITY

MOLECULAR ROTATION “radio” emissions DE = hn

Atmospheric junk Learn: molecular concentrations, temperature, overall density, turbulent and thermal motions, rotation

Dust particles contain 1% of interstellar matter.

MOLECULAR VIBRATIONS Infrared absorption

Rate Coefficients A + B  C + D k = < s v > = A(T) exp(-Ea/kBT)

Cosmic rays produce ions some radical-stable reactions Cosmic rays produce ions

Successes for quiescent cores: Reproduces up to 80% of abundances including ions, radicals, isomers

(diffusion)

Some Star-forming Regions quiescent cores (TMC-1; gas-grain) pre-stellar cores (L1544; gas-grain) low mass protostars (IRAS 16293-2422) protoplanetary disks (DM Tau; gas + accret./desorp.) hot cores (Orion KL; gas-grain)

Protoplanetary Disk (Proplyd) Column density Cosmic rays UV X-ray midplane UV 500 AU 0.01-0.1 M0 T Tauri star – 106 yr old Keplerian rotation

Temperature and Density Distribution (D’Alessio et al. 1998, 1999) A. MIDPLANE Radius (AU) n(cm-3) T (K) 1 10(14) 600 10 10(12) 50 Heavy species condensed onto grains 100 10(9) 20 400 10(7) 10

Gaseous Molecular Abundances ● Molecular Line Survey at IRAM30m telescope (Dutrey et al. 1997) Abundance relative to H2 Species Disk(DMTau) Cloud(TMC1) CO 1.4 × 10-5 7 × 10 -5 HCN 5.5 × 10 -10 2 × 10 -8 CN 3.2 × 10 -9 3 × 10 -8 CS 3.3 × 10 -10 1 × 10 -8 H2CO 2.0 × 10 -10 2 × 10 -8 HCO+ 7.4 × 10 -10 8 × 10 -9 C2H 1.1 × 10 -8 8 × 10 -8 Gaseous molecular abundances in disks are different from those in clouds, typically lower, but these are averages in outer disk.

Details of Models Collaborators: Aikawa, van Dishoeck, van Zadelhof Divide outer disk into elements of space; each with density and temperature. Do chemistry over 106 yr in each element. Collaborators: Aikawa, van Dishoeck, van Zedelhof

Vertical Distribution Ｒ＝１０５ＡＵ temperature density 70 60 50 40 30 20 T [K] 109 108 107 106 105 70 K 60 50 40 30 20 109 cm-3 108 107 106 105 R = 105 AU densiy [cm-3] photodissociation 0 20 40 60 80 100 Z(AU) accretion Too detailed for observers Icy Layer Molecular Layer PDR