Table 1: Overview of the processes included in the ISM model used. For H and He ionization equilibrium is explicitly calculated, for other elements collisional ionization equilibrium (CIE) is assumed. Both the heating and cooling strongly depend on the ionization fraction $x_{\rm e}$ . Exact expressions adopted for the various processes can be found in: 1) Wolfire et al. (1995); 2) Raga et al. (1997); 3) Verner & Ferland (1996); 4) Silva & Viegas (2001).
Process Comment Ref.

Heating

  Cosmic Ray ionization rate $\rm\zeta_{CR}=1.8$ $\times$ $10^{-17}~{\rm s}^{-1}$ 1

  Photo Electric FUV field from stars 1

Cooling

  e,H₀ impact H, He, C, N, O, Si, Ne, Fe 2, 4

Ionization

& recombination

  UV ionization assumed for

species with $E_i< 13.6 \rm {eV}$

  Cosmic Ray H, He only; primary 1

& secondary ionizations

  Collisional H, He only 3

  Radiative recombination H, He only 3

  CIE assumed for metals

**Table 1:** Overview of the processes included in the ISM model used. For H and He ionization equilibrium is explicitly calculated, for other elements collisional ionization equilibrium (CIE) is assumed. Both the heating and cooling strongly depend on the ionization fraction $x_{\rm e}$ . Exact expressions adopted for the various processes can be found in: 1) Wolfire et al. (1995); 2) Raga et al. (1997); 3) Verner & Ferland (1996); 4) Silva & Viegas (2001).
Process	Comment	Ref.
Heating
Cosmic Ray	ionization rate $\rm\zeta_{CR}=1.8$ $\times$ $10^{-17}~{\rm s}^{-1}$	1
Photo Electric	FUV field from stars	1
Cooling
e,H₀ impact	H, He, C, N, O, Si, Ne, Fe	2, 4
Ionization
& recombination
UV	ionization assumed for
	species with $E_i< 13.6 \rm {eV}$
Cosmic Ray	H, He only; primary	1
	& secondary ionizations
Collisional	H, He only	3
Radiative recombination	H, He only	3
CIE	assumed for metals

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