Presentation on theme: "The Future of Astrochemistry"— Presentation transcript:
1 The Future of Astrochemistry Eric HerbstDepartments of Physics, Astronomy, and ChemistryThe Ohio State UniversityIt’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 knowThere are known unknowns.That is to say,We know there are some thingsWe do not know.But there are also unknown unknowns,The ones we don’t knowWe don’t know.
3 Interstellar MediumGas (99%) and tiny dust particles (1%) mainly in the form of “clouds” (old term “nebulae”)Clouds range from diffuse (starlight shines through) to denseIn “giant” clouds, both diffuse and dense regions existInterstellar matter arises from matter expelled from old starsDense interstellar matter collapses to form new starsDense clouds are almost entirely molecular!!! Molecules make good probes, both via spectroscopy and chemical models.
4 Some Future ProspectsI) New and interesting molecules in the interstellar gas and grain mantlesII) Better understanding of relevant chemical processes including surface chemistryIII) Much better understanding of heterogeneity and dynamics of individual sources, and stellar and planetary formationIV) More research on extra-galactic sources
5 I. NEW MOLECULES150 + isotopomers already known in gas (2-13 atoms); 10 in ice mantles; PAH’sNormal, 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 linesCan 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) P132. a radical new technique to account for the intensities of unanalyzed lines T13
9 Possible New Species Small hydrides (LiH) Unusual molecules (HOCN, HCNO) P08Biotic species (glycine?) T08, T10Very large organic species (fullerenes?) P10 P17,T11-12Large negative ions (PAH-)Doubly charged ions (CO2+)Molecules in ice mantles P01, P15
11 Poorly Understood Chemical Processes/Regimes Some barrierless reactions T14Negative ion formation and depletion P02High temperature chemistry and path to thermal equilibriumFormation and chemistry of very large molecules T12Non-thermal desorption mechanisms T07Diffusive and other surface reactive mechanismsCoagulation, 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 DYNAMICSALMA: the future…….following BIMA, CARMA, SMA…. (T05)
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 occursSome major ice features can be reproduced (H2O, CO, CO2?); saturated organic ices predictedStochastic methods needed for quantitative reproduction of surface chemistry but not yet quite useable.
22 The Real TMC-1Now 6 cores: A, B, C, CP, D, E of different chemical ages (10 – 10 yr ?)
23 Hot Core/Corinos T05 (Sgr B2(N-LMH), Ori KL, IRAS 16293 2422) T= KWarm-up to KevaporationSurface chemistryGas: unsaturated speciesSaturated gas-phase chemistry to more complex speciesSurface: 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 phases1-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, T06Protoplanetary disks (complex molecules, structure; coagulation) T02, P06Galactic center clouds (rich in oxygen-containing organic molecules but not as hot as hot cores)Infra-red Dark Clouds