1. The Future of Astrochemistry
Eric Herbst
Departments of Physics, Astronomy, and Chemistry
The Ohio State University
It’s a molecular universe but there is still much to learn!!!

2. The Unknown As we know, There are known knowns.
There are things we know we know.
We also know
There are known unknowns.
That is to say,
We know there are some things
We do not know.
But there are also unknown unknowns,
The ones we don’t know
We don’t know.

3. Interstellar Medium
Gas (99%) and tiny dust particles (1%) mainly in the form of “clouds” (old term “nebulae”)
Clouds range from diffuse (starlight shines through) to dense
In “giant” clouds, both diffuse and dense regions exist
Interstellar matter arises from matter expelled from old stars
Dense interstellar matter collapses to form new stars
Dense clouds are almost entirely molecular!!! Molecules make good probes, both via spectroscopy and chemical models.

4. Some Future Prospects
I) New and interesting molecules in the interstellar gas and grain mantles
II) Better understanding of relevant chemical processes including surface chemistry
III) Much better understanding of heterogeneity and dynamics of individual sources, and stellar and planetary formation
IV) More research on extra-galactic sources

5. I. NEW MOLECULES
150 + isotopomers already known in gas (2-13 atoms); 10 in ice mantles; PAH’s
Normal, unsaturated, +/- ions, radicals, isomers

6. Ori KL Survey (CSO; hot cores)
(submillimeter-wave rotational spectrum)
“Beware the weeds, my observers! The torsions that bite, the congestion that catches…”

7. WEEDS, CONT.
Mainly internal rotor species (e.g. CH3OH) with thousands of interstellar lines
Can possibly be removed/accounted for by two methods:
1. classical spectroscopic techniques of measuring and analyzing lines, then fitting to a Hamiltonian and predicting new lines etc. (often tabulated in databases) P13
2. a radical new technique to account for the intensities of unanalyzed lines T13

9. Possible New Species Small hydrides (LiH)
Unusual molecules (HOCN, HCNO) P08
Biotic species (glycine?) T08, T10
Very large organic species (fullerenes?) P10 P17,T11-12
Large negative ions (PAH-)
Doubly charged ions (CO2+)
Molecules in ice mantles P01, P15

10. II. RELEVANT CHEMICAL PROCESSES

11. Poorly Understood Chemical Processes/Regimes
Some barrierless reactions T14
Negative ion formation and depletion P02
High temperature chemistry and path to thermal equilibrium
Formation and chemistry of very large molecules T12
Non-thermal desorption mechanisms T07
Diffusive and other surface reactive mechanisms
Coagulation, settling of grains T02

12. Negative Ion Chemistry
Radiative attachment (Herbst 1981); statistical theory leads to radical ions with large electron affinities and more than 4 atoms; e.g.,
C6H + e  C6H- + hn

13. III. EVOLUTION, HETEROGENEITY
AND DYNAMICS
ALMA: the future…….following BIMA, CARMA, SMA…. (T05)

14. IIIA. STAR FORMATION

15. Low-mass Star Formation
Cold Core
Low-mass Star Formation
Pre-stellar Core
stellar
Isothermal collapse
Diffuse
n = 104 cm-3
T = 10 K
Exotic molecules
adiabatic
Protostar
Star + Disk
Cold envelope
hot corino
100 K
Normal organic molecules

16. High-Mass Star Formation
???
Hot core (300 K)
HII region
IR dark cloud

17. IIIB. INDIVIDUAL SOURCES
Chemistry, heterogeneity, dynamics

18. The Case of TMC-1
CO J=10

19. TMC-1 Gas-phase Models: the past?
one-point (0-D) models dominated by ion-molecule reactions with 1000’s of reactions (many not studied); simulations lead to exotic and unsaturated molecules.
Pseudo-time-dependent: lifetime of perhaps 10(5-6) yr “early time” best

20. Gas-grain models: The Future?
Ices build up by accretion and surface chemistry as gas-phase chemistry occurs
Some major ice features can be reproduced (H2O, CO, CO2?); saturated organic ices predicted
Stochastic methods needed for quantitative reproduction of surface chemistry but not yet quite useable.

21. Chemistry and Core Formation
Hear talk T03

22. The Real TMC-1
Now 6 cores: A, B, C, CP, D, E of different chemical ages (10[5] – 10[7] yr ?)

23. Hot Core/Corinos T05 (Sgr B2(N-LMH), Ori KL, IRAS 16293 2422)
T= K
Warm-up to K
evaporation
Surface chemistry
Gas: unsaturated species
Saturated gas-phase chemistry to more complex species
Surface: more saturated species (e.g. CH3OH)

24. Current & Future Models
One-point models directed at organic chemistry (Garrod & Herbst 2006; Garrod et al. 2008; Hassel et al. 2008) with three phases
1-D Hydrodynamic multi-point models (Aikawa et al. 2008)
Models with non-spherical structure, lots of organic chemistry, leading to disks, etc.

25. Other Interstellar Sources
Diffuse interstellar medium (CH+, z, H3+, polyatomics) P04, T06
Protoplanetary disks (complex molecules, structure; coagulation) T02, P06
Galactic center clouds (rich in oxygen-containing organic molecules but not as hot as hot cores)
Infra-red Dark Clouds

26. IV. EXTERNAL GALAXIES

27. A ULIRG galaxy……
Molecules such as HCN and CH2NH claimed in Arecibo GHz survey (Minchin et al AJ?)

28. The Future Known Unknowns:
New molecules, new kinetics, more structure and dynamics, more detailed chemical models, more knowledge of stellar formation
Unknown unknowns ?????????????

29. The Far-Infrared
The soon-to-be Herschel Space Observatory

30. NO SHORTAGE OF CHEMICAL, PHYSICAL, ASTRONOMICAL PROBLEMS WAITING TO BE SOLVED!!!!!!!!!!!!!