J/A+AS/121/139 UMIST database. 1995 (Millar+, 1997)
The UMIST database for astrochemistry 1995.
Millar T.J., Farquhar P.R.A., Willacy K.
<Astron. Astrophys. Suppl. Ser. 121, 139 (1997)>
=1997A&AS..121..139M 1997A&AS..121..139M
ADC_Keywords: Atomic physics ; Interstellar medium
Keywords: ISM: molecules - molecular data - molecular processes
Abstract:
We report the release of a new version of the UMIST database for
astrochemistry. The database contains the rate coefficients of 3864
gas-phase reactions important in interstellar and circumstellar
chemistry and involves 395 species and 12 elements. The previous
(1990, Millar et al. 1991A&AS...87..585M 1991A&AS...87..585M) version of this database has
been widely used by modellers. In addition to the rate coefficients,
we also tabulate permanent electric dipole moments of the neutral
species and heats of formation. A numerical model of the chemical
evolution of a dark cloud is calculated and important differences to
that calculated with the previous database noted.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
rate95.dat 78 3864 Reactions and their rate coefficients
(updated 5/03/96, table 4 of the paper)
dipole94.dat 26 136 Electric dipole moments for neutral molecules
contained in the reaction library
(last update 12-06-95, table 3 of the paper)
heats94.dat 61 411 *Heats of formation for interstellar species
refs.dat 180 186 References of rate95.dat
prog/* . 4 Fortran program and associated file to generate
chemical rate equations and appropriate
conservation equations for a given reaction set
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Note on heats94.dat: Data from H-H Lee (Dept of physics, Ohio State University)
release date 12th June 1995
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Byte-by-byte Description of file: rate95.dat
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Bytes Format Units Label Explanations
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2- 5 I4 --- I Reaction number (1)
7- 13 A7 --- R1 First reactant
15- 21 A7 -- R2 Second reactant (2)
23- 29 A7 --- P1 First reaction product
31- 36 A6 --- P2 Second reaction product
39- 41 A3 --- P3 Third reaction product
43- 44 A2 --- P4 4th reaction product
46- 53 E8.2 --- alpha α coefficient (3)
55- 59 F5.2 --- beta β coefficient (3)
61- 68 F8.1 --- gamma γ coefficient
69 A1 --- M [M] M: rate coefficient measured in
laboratory or deduced (4)
70- 71 A2 --- TR Type of reaction (5)
72 A1 --- EA [EA] relevance of a reaction (6)
73 I1 --- q_I [1/5]? Accuracy of the data (7)
74- 77 A4 --- r_I Source of the data in refs.dat file (8)
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Note (1): Type of reactions:
Reactions 1 - 394: Neutral-neutral reactions
Reactions 395 - 3197: Ion-neutral reactions, including reactions of
positive and negative ions
Reactions 3198 - 3634: Electron reactions, including radiative
electron attachment of H, C, O and S, as well
as radiative and dissociative recombination of
positive ions.
Reactions 3635 - 3645: Ionisation by cosmic-ray protons.
Reactions 3646 - 3795: Photoreactions driven by the interstellar UV
radiation field.
Reactions 3796 - 3864: Cosmic-ray-induced photoreactions.
Note (2): CRP: cosmic-ray proton
PHOTON: a general interstellar ultraviolet photon
CRPHOT: or a cosmic-ray-induced ultraviolet photon
Note (3): For each reaction, the rate coefficient can be calculated as:
k = α(T/300)βexp(-γ/T) cm3/s
for two-body reactions, where T is the gas kinetic temperature,
k = αs-1
for direct cosmic-ray ionisation (R2 = CRP),
k = αexp(-γAV)s-1
for interstellar photoreactions (R2 = PHOTON), where α
represents the rate in the unshielded interstellar UV radiation
field, and γ is the parameter used to take into account the
extinction of the UV radiation by dust particles, and
k = αγ(1-ω)s-1
for cosmic-ray-induced photoreactions (R2 = CRPHOT), where ω is
the grain albedo in the far UV, typically 0.6 at 150nm, and γ
is the probability per cosmic-ray ionisation that the appropriate
photoreaction occurs.
Note (4): An 'M' here means that the rate coefficient has been measured
in the laboratory or, in the case of radiative association, has been
deduced with the aid of an experiment on the analogous three-body
association. For ion-neutral reactions, the rate coefficients are
generally independent of temperature. An important exception are those
reactions in which the neutral molecule has a large, say greater than
1 Debye, permanent electric dipole moment. In such cases, the rate
coefficients generally increase at low temperatures (Adams et al.,
1985ApJ...296L..31A 1985ApJ...296L..31A).
The file dipole94.dat gives electric dipole moments, where available,
for the neutral species in the database. Neutral-neutral reactions are
usually studied experimentally at room temperature and above and
therefore application of laboratory-determined rate coefficients to
the low temperature environments of interstellar clouds is fraught
with uncertainty. For example, it is possible that several reactions
listed in the ratefile as not possessing an activation energy do, in
fact, have small barriers (<100K) which are not evident in
measurements done at room temperature and above. In addition, some
experimental data are best characterised, in the temperature range
over which they are studied, by a negative activation energy barrier.
In order to prevent a serious overestimate of these rate coefficients
at 10K, we have generally preferred to adopt an alternative, although
still accurate, form for the rate coefficients.
Note (5): A two-letter symbol for the type of reaction. The symbols used are:
AD: associative detachment
CD: collisional dissociation
CH: chemi-ionisation
CI: carbon insertion, involving a reaction between a carbon atom and
a hydrocarbon ion
CP: cosmic-ray-induced photoreaction
CO: positive ion-neutral reaction in which H and/or H2 are the only
neutral products
CR: cosmic-ray ionisation
CT: charge transfer
DR: dissociative recombination with electrons
HA: hydrogen abstraction
MN: mutual neutralisation
NA: neutral radiative association
NE: neutral exchange
NI: negative ion-neutral
PD: photodissociation
PI: photoionisation
PM: photodetachment of electron; PN, positive ion-neutral
PT: proton transfer
RA: radiative association between a positive ion and a neutral molecule
RM: radiative electron (minus ion) attachment
RR: radiative recombination with electrons
Note (6): A label is used to denote the relevance of a reaction.
In many instances the user will be interested in using only a subset
of the reaction file rate95.dat, and may want, for ease of computation
and analysis, to neglect unimportant reactions. Certain types of
reaction may be excluded from a particular model. For example,
reactions with large activation energy barriers, which are important
in shocked gas, and photoreactions can be neglected in models of cold,
dark clouds. In addition, however, there are reactions whose neglect
will not seriously compromise the results of most models. These are
labelled with an 'E' in this column. This category is most used for
ions, such as NH+ and H2O+, which have rapid reactions with
H2. The low abundance of all other species X relative to H2 in
many astronomical regions, means that all ion-X reactions can be
excluded. This criterion is only useful if H2 is the dominant form
of hydrogen. If a reaction should be included in any comprehensive
model it is labelled with an 'A'.
Note (7): A digit is used to represent the accuracy of the data.
We have used such labelling mainly for the ion-neutral and
photoreactions, although sometimes the accuracy of the formula given
may be restricted to a particular range of temperature. The following
scheme has been used:
1. Error < 25 %
2. Error < 50 %
3. Error to within a factor of 2
4. Error within an order of magnitude
5. Highly uncertain
We have not attempted to give the accuracy of the unmeasured
reactions. The ion-neutral rate coefficients should be accurate to a
factor of two, but it is possible that some of the reactions included
here have different products or are unreactive.
Note (8): A label to the source of the data.
Labels of the form '8010' refer to the labelling scheme of Anich and
Huntress (1986ApJS...62..553A 1986ApJS...62..553A). An explanation of the letter codes,
such as RJ91, are listed in the refs.dat file.
The label 'NIST', used for many of the neutral-neutral reactions,
refers to the National Institute of Standards and Technology Chemical
Kinetics Database - Ver. 6.0 (Mallard et al. 1994).
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Byte-by-byte Description of file: dipole94.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Species Species (1)
17 A1 --- --- [^]
18 A1 --- l_mu Limit flag on mu
19- 23 F5.3 D mu ? Electric dipole moment
25- 26 A2 --- Note Notes (2)
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Note (1): Notes on species:
C3S from (Suenram & Lovas), 1994ApJ...429L..89S 1994ApJ...429L..89S
CH3C3N and CH3C5N from Botschwina et al., 'Molecules and grains
in space', (Ed I Nenner), P. 321 (1994)
H2CCCC from Oswald & Botschwina, 1995, J. Mol. Spectrosc, 169, 181
H2C3H from Botschwina, Oswald, Flugge, & Horn, 1995,
Zeit. Phys. Chem., 188, S. 29
C5O = 4.06 D (Botscwina, Flugge & Sebald, 1995, JPC, Submitted)
Note (2): Individual notes
* l - C3H , c - C3H = 2.4 D
** c - C3H2, H2CCC = 4.1 D
$ HCCCCH, H2CCCC = 4.5 D
@ H2C3H(PROPARGYL) = 0.14 D
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Byte-by-byte Description of file: heats94.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Species Species
10- 15 F6.1 kJ/mol FH298K ? Formation heat at 298K (in kJ/mole)
18- 23 F6.1 kJ/mol FH0K ? Formation heat at 0K (in kJ/mole)
27- 31 F5.1 kJ/mol e_FH0K ? rms uncertainty on FH0K
32 A1 --- n_FH0K [*&] Note on FH0K (1)
34- 39 F6.1 kJ/mol FHiso1 ? Formation heat for first isomer
42- 43 I2 kJ/mol e_FHiso1 ? rms uncertainty on FHiso1
44 A1 --- n_FHiso1 [&] Note on FHiso1 (1)
46 I1 --- r_FHiso1 [1]? 1: FHiso1 from Gingerich et al.
1994, JACS, 116, 3384
49- 54 F6.1 kJ/mol FHiso2 ? Formation heat for second isomer
55 A1 --- n_FHiso2 [&] Note on FHiso2 (1)
56 A1 --- --- [*]
58- 60 I3 --- Seq Sequential number
61 A1 --- --- [*]
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Note (1): Notes:
*: when formation heats are the same at 0 and 298K
&: not explicited
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- Ref Reference code
7- 25 A19 --- BibCode BibCode
27- 50 A24 --- Aut Author names
53-180 A128 --- Com Comments
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History:
Copied at http://saturn.phy.umist.ac.uk:8000/~tjm/rate/rate.html
(End) Patricia Bauer [CDS] 16-Nov-2000