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

9. MOLECULAR ROTATION
“radio” emissions
DE = hn

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

12. Dust particles contain 1% of interstellar matter.

14. MOLECULAR VIBRATIONS
Infrared absorption

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

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

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

23. (diffusion)

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

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

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

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

28. 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

29. 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
Z(AU)
accretion
Too detailed for observers
Icy
Layer
Molecular
Layer
PDR