4 Other data

4.1 Deuterium chemistry

A comprehensive description of deuterium chemistry requires that all D-bearing analogues of H-bearing species are included in a chemical model. This has the effect of approximately tripling the number of reactions in a model if it is to include deuterium. For our purposes, we have decided not to include a full deuterium chemistry in this release. Such a chemistry can be generated most efficiently using software but the detailed branching ratios adopted are a matter of individual choice at this time and we prefer to list only the most important reactions in Table 6. Rodgers & Millar (1996) have discussed many of the issues involved in generating a deuterium chemistry.

 

 

Table 5: List of the types of chemical reactions and their position in the database. The unclassifiable reactions are put in the category "Sundries''. The first column XX is the abbreviation used for the types

XX	Type of	Position
	reaction	(index "I'')
NN	Neutral - Neutral Reactions	1	-	433
IN	Ion - Neutral Reactions	434	-	2606
CE	Charge Exchange Reactions	2607	-	3144
II	Ion - Ion Neutralisations	3145	-	3175
DR	Dissociative Recombinations	3176	-	3606
RR	Radiative Recombinations	3607	-	3631
AD	Associative Detachments	3632	-	3678
RA	Radiative Associations	3679	-	3760
PH	Photoprocesses	3761	-	3916
CP	Cosmic-Ray Proton Reacs (CRP)	3917	-	3927
CR	Cosmic-Ray Photon Reacs (CRPHOT)	3928	-	4059
CL	Collider Reactions	4060	-	4077
TR	Termolecular Reactions	4078	-	4107
-	Sundries	4108	-	4113

 

 

Table 6: Deuterium Reactions. NOTE: a(b) stands for a$\times$10^b. (D-resc) means that the equivalent H-only reaction rate has been rescaled by D reduced mass. ^* implies that the exponential term in the rate expression has the form exp($-T/\gamma$). References: as: Adams & Smith 1985; cd: Crosswell & Dalgarno 1985; dl: Dalgarno & Lepp 1987; dmd: Dalgarno & McDowell 1956; fp: Frommhold & Pickett 1978; hasd: Herbst et al. 1987; kah: Karpas et al. 1979; lbh: Lee et al. 1996; ljb: Linder et al. 1995; lm: Larsson et al. 1996; pdf: Pineau des Forêts et al. 1986; rp: Ramaker & Peek 1976; s: Schilke et al. 1992; saa: Smith et al. 1982a,b; smt: Sidhu et al. 1992; str: Strömholm et al. 1995; w: Watson 1976; zm: Zhang & Miller 1989

Reaction							$\alpha$ (cm3 s-1)	$\beta$	$\gamma$ (K)	References
H3+	+	HD	$\rightarrow$	H2D+	+	H2	1.5(-09)			lbh
H2D+	+	H2	$\rightarrow$	H3+	+	HD	2.0(-09)	-0.8	230	smt
CH2+	+	HD	$\rightarrow$	CH2D+	+	H2	1.3(-09)	-	-	saa
CH2D+	+	H2	$\rightarrow$	CH2+	+	HD	8.7(-10)	-	370	saa
C2H2+	+	HD	$\rightarrow$	C2HD+	+	H2	1.0(-09)	-	-	hasd
C2HD+	+	H2	$\rightarrow$	C2H2+	+	HD	2.5(-09)	-	550	hasd
D+	+	H2	$\rightarrow$	H+	+	HD	2.1(-09)	-	-	saa
H+	+	HD	$\rightarrow$	D+	+	H2	1.0(-09)	-	464	saa
D+	+	H	$\rightarrow$	H+	+	D	1.0(-09)	-	-	w
H+	+	D	$\rightarrow$	D+	+	H	1.0(-09)	-	41	w
H3+	+	D	$\rightarrow$	H2D+	+	H	1.0(-09)	-	-	as (estimate)
H2D+	+	H	$\rightarrow$	H3+	+	D	1.0(-09)	-	632	as (estimate)
HCO+	+	D	$\rightarrow$	DCO+	+	H	1.0(-09)	-	-	as
DCO+	+	H	$\rightarrow$	HCO+	+	D	2.2(-09)	-	796	as
N2H+	+	D	$\rightarrow$	N2D+	+	H	1.0(-09)	-	-	as
N2D+	+	H	$\rightarrow$	N2H+	+	D	2.2(-09)	-	550	as
OH	+	D	$\rightarrow$	OD	+	H	1.3(-10)	-	-	cd
OD	+	H	$\rightarrow$	OH	+	D	1.3(-10)	-	810	cd
N+	+	HD	$\rightarrow$	ND+	+	H	3.2(-10)	-	16	s
N+	+	HD	$\rightarrow$	NH+	+	D	3.2(-10)	-	100	s
C2H	+	D	$\rightarrow$	C2D	+	H	5.0(-11)	0.5	250	s
C2D	+	H	$\rightarrow$	C2H	+	D	5.0(-11)	0.5	832	s
HCN	+	D	$\rightarrow$	DCN	+	H	1.0(-10)	0.5	500	s (estimate)
DCN	+	H	$\rightarrow$	HCN	+	D	1.0(-10)	0.5	500	s (estimate)
D+	+	D-	$\rightarrow$	D	+	D	5.7(-08)	-0.5	-	dl (D-resc)
D+	+	H-	$\rightarrow$	D	+	H	4.6(-08)	-0.5	-	dl (D-resc)
H+	+	D-	$\rightarrow$	D	+	H	4.6(-08)	-0.5	-	dl (D-resc)
D	+	H-	$\rightarrow$	H	+	D-	6.4(-09)	0.41	-	dmd (D-resc)
H	+	D-	$\rightarrow$	D	+	H-	6.4(-09)	0.41	-	dmd (D-resc)
H2+	+	D	$\rightarrow$	HD+	+	H	1.07(-09)	0.06	41400*	ljb
H2+	+	D	$\rightarrow$	H2	+	D+	6.4(-10)	-	-	kah
HD+	+	H	$\rightarrow$	H2+	+	D	1.0(-09)	-	154	dmd (D-resc)
HD+	+	e-	$\rightarrow$	H	+	D	3.4(-09)	-0.4	-	str
HD+	+	H	$\rightarrow$	HD	+	H+	6.4(-10)	-	-	kah
HD+	+	H2	$\rightarrow$	H3+	+	D	1.05(-09)	-	-	pdf
H	+	D+	$\rightarrow$	HD+	+	h$\nu$	3.9(-19)	1.8	-20	rp (D-resc) + fp
D	+	H+	$\rightarrow$	HD+	+	h$\nu$	3.9(-19)	1.8	-20	rp (D-resc) + fp
H2	+	D	$\rightarrow$	HD	+	H	7.5(-11)	-	3820	zm (fitted)
HD	+	H	$\rightarrow$	H2	+	D	7.5(-11)	-	4240	zm (fitted)
H2	+	D+	$\rightarrow$	H2D+	+	h$\nu$	1.0(-20)	-	-	dmd (D-resc)
HD	+	H+	$\rightarrow$	H2D+	+	h$\nu$	1.0(-20)	-	-	dmd (D-resc)
H2+	+	D	$\rightarrow$	H2D+	+	h$\nu$	7.0(-18)	1.8	-20	dmd (D-resc)
HD+	+	H	$\rightarrow$	H2D+	+	h$\nu$	1.2(-17)	1.8	-20	dmd (D-resc)
H2D+	+	e-	$\rightarrow$	H         +	H	+ D	4.38(-08)	-0.5	-	lm
H2D+	+	e-	$\rightarrow$	H2	+	D	4.2(-09)	-0.5	-	lm
H2D+	+	e-	$\rightarrow$	H	+	HD	1.2(-08)	-0.5	-	lm
HD+	+	H2	$\rightarrow$	H2D+	+	H	1.05(-09)	-	-	pdf
HD	+	H2+	$\rightarrow$	H2D+	+	H	1.05(-09)	-	-	dmd (D-resc)
HD	+	H2+	$\rightarrow$	H3+	+	D	1.05(-09)	-	-	dmd (D-resc)

 

 

Table 7: List of the species for which photo processes can be derived using known cross sections. The photo processes are calculated only from the ground state

Species	Processes	Products	References
He	ionisation	He+ + e-	Band et al. 1990
C	ionisation	C+ + e-	Cantù et al. 1981, Hofmann et al. 1983
C+	ionisation	C++ + e-	Henry 1970
C++	ionisation	C3+ + e-	Osterbrock 1974
N	ionisation	N+ + e-	Henry 1970
O	ionisation	O+ + e-	Taylor & Burke 1976, Henry 1970
Ne	ionisation	Ne+ + e-	Henry 1970
Si	ionisation	Si+ + e-	Chapman & Henry 1972
C2	ionisation	C2+ + e-	Padial et al. 1985
	dissociation	C + C	Pouilly et al. 1983
CO	ionisation	CO+ + e-	Hudson 1971
	dissociation	C + O	Letzelter et al. 1987
CO2	ionisation	CO2+ + e-	Hudson 1971, Hitchcock et al. 1980
	fragmentation	CO + O+ + e-	Hitchcock et al. 1980
		O + CO+ + e-	Hitchcock et al. 1980
		O2 + C+ + e-	Hitchcock et al. 1980
O2	ionisation	O2+ + e-	Brion & Tan 1979, Ogawa & Ogawa 1975,
			Clarke & Wayne 1970
	fragmentation	O + O+ + e-	Brion & Tan 1979
N2O	ionisation	N2O+ + e-	Hitchcock et al. 1980
	fragmentation	NO+ + N + e-	Hitchcock et al. 1980
	fragmentation	NO + N+ + e-	Hitchcock et al. 1980
	fragmentation	N2+ + O + e-	Hitchcock et al. 1980
	fragmentation	N2 + O+ + e-	Hitchcock et al. 1980

4.2 Cross sections for photoprocesses

The necessity for having data on photo process cross sections arises from the fact that astrochemistry is not exclusive to the ISM but is now applied to circumstellar regions and comets as well. As a result, the rates of destruction of the species through exposure to the stellar radiation field can change by several orders of magnitude. For example, the photoionization rate of He⁰ in interstellar clouds is negligible, whereas in the radiation field of a nearby Wolf-Rayet star it can be as large as 10^-5 s^-1. Table 7 gives the list of the species and the data references compiled to date by us. The detailed cross-sections, which are available electronically, are given in megabarns (1 Mb = 10^-18 cm²). The photorate, $\beta(X,r)$ (s^-1), for species X at a distance r from a localised radiation source can be derived using Eq. (5):

$$\beta (X,r) = \frac{10^{-26}\;w(r)}{hc}\int_{\lambda<\lambda_... ... {\cal F}_{\lambda} \; \sigma_{\lambda}(X) \; \mbox{d}\lambda$$ (5)

where w(r) is the dilution factor at the distance r from the source, $\lambda_0$ (Å) is the photoprocess threshold wavelength, such that any photon with $\lambda<\lambda_0$ will take part to the process, ${\cal F}_{\lambda}$ is the source Spectral Energy Distribution in erg cm^-2 s^-1 Å ^-1, $\sigma_{\lambda}(X)$ is the cross section (Mb) for the species X at the wavelength $\lambda$ (Å).

These data are not complete. Future work is aimed at updating these via the Opacity Project and other sources.

4.3 Dipole moments

At low temperatures, the rates of ion-molecule reaction rate coefficients can increase dramatically through ion-dipole interactions, which are particularly important for the interaction of light ions with neutrals possessing a permanent electric dipole moment in excess of about 1 Debye. Table 3 gives electric dipole moments for the neutral molecules contained in this database.