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Table 1

Overview of the most important model parameter.

Parameter Value(s) Comments Reference

Gridpoints

{Mcl} 10iM with i = −3,−2,...,3 clump mass
{ns} 10i cm-3 with i = 3,4,...,7a clump surface density
{IUV} 10iχ0 with i = −1,0,...,6 FUV scaling factor

Abundances relative to the total hydrogen abundance

He/H 0.0851 (1)
O/H 4.47(−4) (2)
C/H 2.34(−4) (2)
13C/H 3.52(−6) based on a 12C/13C ratio of about 67 in Orion (3)
S/H 7.41(−6) (2)

Others

α 1.8 clump-mass power law index (4)
γ 2.3 mass-size power law index (4)
Z 1 solar metallicity
ζ CR 2(−16) s-1 cosmic ray primary ionisation rate per H2 (5)
RV 5.5b ratio between visual extinction and “reddening” (6)
for dense clouds
σg 8.41(−22) cm2 FUV dust cross section per H (7)
b 1 km s-1 Doppler broadening parameterc
AV/NH 5.3(−22) cm2 normalisation for extinction curve (8)

Notes. The numbers in parentheses indicate powers of ten.

(a)

For densities higher than 107 cm-3 the steep chemical gradient and short reaction time scales can cause numerical problems.

(b)

Correspondingly, we use an averaged, normalised extinction kFUV = ⟨ A(λ) /A(V) ⟩ λ = 1.722 with λ = 912...2066 Å (Röllig et al. 2013).

(c)

b = FWHM/ (4 ln 2)1/2, i.e. b = 1 km s-1 corresponds to FWHM = 1.67 km s-1 (Draine & Bertoldi 1996).

Reference. (1) Asplund et al. (2005); (2) Simón-Díaz & Stasińska (2011); (3) Langer & Penzias (1990); (4) Heithausen et al. (1998); (5) Hollenbach et al. (2012); (6) Draine & Bertoldi (1996); (7) Röllig et al. (2013); (8) Weingartner & Draine (2001a).

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