Slide 1 - The Midwest Astrochemistry Consortium

							   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!!!
               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.
            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.
      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
          I. NEW MOLECULES
150 + isotopomers already known in gas
(2-13 atoms); 10 in ice mantles; PAH’s
 Normal, unsaturated, +/- ions, radicals, isomers
        Ori KL Survey (CSO; hot cores)
       (submillimeter-wave rotational spectrum)




“Beware the weeds, my observers! The torsions that bite,
the congestion that catches…”
           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
        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
II. RELEVANT CHEMICAL
PROCESSES
    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
     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
III. EVOLUTION, HETEROGENEITY
          AND DYNAMICS




  ALMA: the future…….following
  BIMA, CARMA, SMA…. (T05)
IIIA. STAR FORMATION
Cold Core                     Low-mass Star            Pre-stellar Core
                                Formation
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
       High-Mass Star Formation


   ???                           Hot core (300 K)
                    HII region




IR dark cloud
 IIIB. INDIVIDUAL SOURCES



Chemistry, heterogeneity,
dynamics
    The Case of TMC-1
CO J=10
   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
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.
Chemistry and Core Formation




Hear talk T03
            The Real TMC-1




Now 6 cores: A, B, C, CP, D, E of different chemical
ages (10[5] – 10[7] yr ?)
             Hot Core/Corinos T05
 (Sgr B2(N-LMH), Ori KL, IRAS 16293 2422)

          T=10-30 K
                           Warm-up to
                           100-300 K



                           evaporation

Gas: unsaturated species   Surface          Saturated gas-
                           chemistry        phase chemistry
Surface: more
saturated species (e.g.                     to more complex
CH3OH)                                      species
     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.
    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
IV. EXTERNAL GALAXIES
                 A ULIRG galaxy……




Molecules such as HCN and CH2NH claimed in Arecibo
1.1-10 GHz survey (Minchin et al. 2008 AJ?)
              The Future
• Known Unknowns:
• New molecules, new kinetics, more
  structure and dynamics, more detailed
  chemical models, more knowledge of
  stellar formation

• Unknown unknowns ?????????????
                 The Far-Infrared




The soon-to-be
Herschel Space
Observatory
  NO SHORTAGE OF
 CHEMICAL, PHYSICAL,
   ASTRONOMICAL
PROBLEMS WAITING TO
  BE SOLVED!!!!!!!!!!!!!