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J/A+A/321/293       SiO production in interstellar shocks        (Schilke+ 1997)
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SiO production in interstellar shocks.
    Schilke P., Walmsley C.M., Pineau des Forets G., Flower D.R.
   <Astron. Astrophys. 321, 293 (1997)>
   =1997A&A...321..293S      (SIMBAD/NED BibCode)
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ADC_Keywords: Interstellar medium ; Atomic physics
Keywords: molecular processes - shock waves -
          ISM: abundances; jets and outflows; molecules

Abstract:
    We study the production of SiO in the gas phase of molecular outflows,
    through the sputtering of Si-bearing material in grains. The
    sputtering is driven by neutral particle impact on charged grains in
    C-type shocks, at the speed corresponding to ambipolar diffusion.
    Shock speeds in the range 10<v_s_<40km/s and preshock densities
    10^4^<n_H_<10^7^cm^-3^ have been investigated. Sputtering of
    Si-bearing material in both the cores and the mantles of the grains is
    considered. We find that, for v_s_ of approximately 25km/s and n_H_ of
    the order 10^5^cm^-3^, column densities of SiO similar to those
    observed in molecular out flow regions can be generated by either
    mechanism. Impact by particles heavier than helium dominates the
    core-sputtering process for shock velocities of this order. The
    profiles of rotational transitions of SiO are computed and compared
    with observations of molecular outflows.

File Summary:
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  FileName      Lrecl  Records   Explanations
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ReadMe             80        .   This file
table1a            72       30  *Mantle and dissociative sputtering parameters
table1b            72       12  *Dissociation on impact parameters
table2             80      100   Rate coefficient parameters, for gas-phase
                                  reactions involving Si-bearing species
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Note on table1a and table1b: Parameters adopted when computing the rate
  coefficients for reactions involving grains
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Byte-by-byte Description of file: table1a
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   Bytes Format Units   Label     Explanations
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       1  A1    ---     Type      [ab] a: mantle sputtering,
                                       b: dissociative sputtering
   3- 15  A13   ---     R1        Beginning species of the reaction (1)
  17- 37  A21   ---     R2        Resulting species of the reaction
  39- 45  E7.2  ---     S         Sputtering yield factor
  48- 52  F5.2  eV      Eth       Sputtering threshold energy
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Note (1): Asterisks denote species in grain mantles
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Byte-by-byte Description of file: table1b
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   Bytes Format Units   Label     Explanations
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       1  A1    ---     Type      [c] c: dissociation on impact
   3- 15  A13   ---     R1        Beginning species of the reaction
  17- 37  A21   ---     R2        Resulting species of the reaction
  39- 45  E7.2  ---     Y0        Multiplicative constant (1)
  48- 52  F5.2  ---     Ediss     Dissociation energy (1)
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Note (1): The dissociative probability has an Arrhenius form, Y0exp(-Ediss/E),
           where E is the impact energy, Ediss the dissociation energy and
           Y0 the multiplicative constant
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Byte-by-byte Description of file: table2
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   Bytes Format Units   Label     Explanations
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   1- 14  A14   ---     R1        Beginning species of the reaction
  16- 32  A17   ---     R2        Resulting species of the reaction
  34- 41  E8.2  ---     gamma     Gamma coefficient (1)
  44- 48  F5.2  ---     alpha     ? Alpha coefficient (1)
  50- 56  F7.1  K       beta      ? Beta coefficient (1)
      58  I1    ---     Note      ? Note (2)
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Note (1): Rate coefficient : gamma.(T/300)^alpha^.exp(-beta/T) cm^3^/s
Note (2): 1: Langer & Glassgold, 1990, ApJ 352, 123
          2: Supposed to be the same as CH (Gredel, 1990)
          3: MacKay, 1995MNRAS.274..694M
          4: UMIST ratefile (Millar et al., 1996, A&AS, in press)
          5: Herbst (1995, private communication)
          6: Elkin & Armentrout, 1984, J. Phys. Chem. 88, 5454
          7: See the discussion of Flower et al., 1996MNRAS.280..447F
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References:
    Gredel R., 1990 in "Molecular astrophysics", Hartquist T.W. ed,
     Cambridge University Press, Cambridge, p.305
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(End)                                         Patricia Bauer [CDS]   30-Sep-1996