title Hollenbach et al. 1991 low-density PDR
iterate 
c
//>>refer Hollenbach, D., Takahashi, T., & Tielens, A.G.G.M., 1991, ApJ,
//>>refercon 377, 192-209
c
hden 3
c
c this is hot star continuum
black 30000
intensity  0.2 range  0.4412 to 1 Ryd
c this will remove all ionizing radiation
extinguish 24 0
c
turbulence 1.5 km/sec
c first continuum is FIR hot grain continuum produced in 
c unmodeled HII Region
// turn on quantum heating
grains orion, abundance log 0.16 
// turn on PAHs using default abundance dependence on physical conditions
grains PAH 
// turn on the big H2 molecule 
atom h2 
init file="ism.ini"
abundances he -1.01 c -3.52 n-8 o-3.30 ne-8 mg-5.89
continue si -6.10 s -5.10 cl-7 ar-8 fe -6.60
normalize to 157.6m "C  2" 
sphere
case b
cosmic rays, background
c stop when gas is fully neutral
stop efrac -10
c this is to stop at an intended place, since results would be
c very dependent on details if we stop on temperature
stop thickness 18.954
c stop when gas is cold
stop temperature 10 linear
c add this to mimic unmodelled neutral gas
double optical depths
c
c uv lines are strongly pumped by stellar continuum, break out contribution
print line pump
print line optical depths
print ages
c
save performance "h2_HTT91.per"
save overview last "h2_HTT91.ovr"
save dr "h2_HTT91.dr"
save molecules last "h2_HTT91.mol"
save results last "h2_HTT91.rlt"
save monitors last "h2_HTT91.asr"
save continuum units microns last "h2_HTT91.con"
save heating last "h2_HTT91.het"
save cooling last "h2_HTT91.col"
save chemistry rates destruction "h2_HTT91.H2d" "H2"
save chemistry rates creation "h2_HTT91.H2c" "H2"
c
// >>chng 12 apr 09, from -2.595 to -2.539, update backbround CR to Indiolo_07 (8x larger)
monitor line luminosity "c  2" 157.6m -2.539
//
// >>chng 05 jun 21, from -3.38 to -3.36, chng cr, grn deex
// >>chng 12 apr 09, from -3.36 to -3.258, update backbround CR to Indiolo_07 (8x larger)
monitor line luminosity "O  1" 63.17m -3.258 error 0.1 
//
// >>chng 11 nov 16, from -2.549 to -2.52, adjust newmole monitors
// >>chng 12 apr 09, from -2.52 to -2.47, update backbround CR to Indiolo_07 (8x larger)
monitor line luminosity "grgh" 0 -2.47
//
// >>chng 12 apr 09, from 68.8 to 74.52, update backbround CR to Indiolo_07 (8x larger)
monitor temperature carbon 2 74.52
//
// >>chng 11 nov 16, from 21.37 to 21.26, adjust newmole monitors
// >>chng 12 apr 09, from 21.26 to 21.21, update backbround CR to Indiolo_07 (8x larger)
monitor column H2 21.21 error 0.1
//
// >>chng 05 jul 17, from 12.85 to 12.35, first run in 6 mo
// >>chng 07 jan 10, from 12.35 to 12.44, H3+ to McCall rates
// >>chng 11 dec 12, from 12.44 to 12.53, bug-fix for updating grain opacity (r5759)
// >>chng 12 apr 09, from 12.53 to 13.32, update backbround CR to Indiolo_07 (8x larger)
monitor column CO 13.32 error 0.2 
// 
// >>chng 11 jul 16, add these
// >>chng 11 jul 16, from 10 to 12.09, add column density monitors
// >>chng 11 nov 16, from 12.09 to 11.97, adjust newmole monitors
// >>chng 12 apr 09, from 11.97 to 12.78, update backbround CR to Indiolo_07 (8x larger)
monitor column density H3+  12.78 error 0.1
// >>chng 11 jul 16, from 10 to 11.21, add column density monitors
// >>chng 11 nov 16, from 11.21 to 11.13, adjust newmole monitors
// >>chng 12 apr 09, from 11.13 to 11.99, update backbround CR to Indiolo_07 (8x larger)
monitor column density H2+  11.99 error 0.1
// >>chng 11 jul 16, from 10 to 10.74, add column density monitors
// >>chng 11 nov 16, from 10.74 to 10.8, adjust newmole monitors
// >>chng 12 apr 09, from 10.8 to 10.91, update backbround CR to Indiolo_07 (8x larger)
monitor column density H-   10.91 error 0.1
// >>chng 11 jul 16, from 10 to 21.34, add column density monitors
// >>chng 11 nov 16, from 21.34 to 21.26, adjust newmole monitors
// >>chng 12 apr 09, from 21.26 to 21.21, update backbround CR to Indiolo_07 (8x larger)
monitor column density H2g  21.21 error 0.1
// >>chng 11 jul 16, from 10 to 15.33, add column density monitors
// >>chng 11 nov 16, from 15.33 to 15.07, adjust newmole monitors
monitor column density H2*  15.07 error 0.1
// >>chng 11 jul 16, from 10 to 10.36, add column density monitors
// >>chng 12 apr 09, from 10.36 to 11.23, update backbround CR to Indiolo_07 (8x larger)
monitor column density HeH+ 11.23 error 0.1
// >>chng 11 jul 16, from 10 to 9.726, add column density monitors
// >>chng 11 nov 16, from 9.726 to 9.791, adjust newmole monitors
// >>chng 12 jan 06, from 9.791 to 9.831, several H2 model changes
// >>chng 12 apr 09, from 9.831 to 10.67, update backbround CR to Indiolo_07 (8x larger)
monitor column density O2   10.67 error 0.1
// >>chng 11 jul 16, from 10 to 11.5, add column density monitors
// >>chng 12 apr 09, from 11.5 to 12.35, update backbround CR to Indiolo_07 (8x larger)
monitor column density H2O  12.35 error 0.1
// >>chng 11 jul 16, from 10 to 12.23, add column density monitors
// >>chng 11 dec 12, from 12.23 to 12.18, bug-fix for updating grain opacity (r5759)
// >>chng 12 apr 09, from 12.18 to 12.05, update backbround CR to Indiolo_07 (8x larger)
monitor column density C2   12.05 error 0.1
// >>chng 11 jul 16, from 10 to 9.56, add column density monitors
// >>chng 11 dec 12, from 9.56 to 9.505, bug-fix for updating grain opacity (r5759)
// >>chng 12 apr 09, from 9.505 to 9.386, update backbround CR to Indiolo_07 (8x larger)
monitor column density C3   9.386 error 0.1
// >>chng 11 jul 16, from 10 to 8.223, add column density monitors
// >>chng 12 apr 09, from 8.223 to 9.04, update backbround CR to Indiolo_07 (8x larger)
monitor column density SiO  9.04 error 0.1
// >>chng 11 jul 16, from 10 to 12.31, add column density monitors
// >>chng 12 apr 09, from 12.31 to 13.11, update backbround CR to Indiolo_07 (8x larger)
monitor column density OH   13.11 error 0.1
// >>chng 11 jul 16, from 10 to 5.834, add column density monitors
// >>chng 11 nov 16, from 5.834 to 5.792, adjust newmole monitors
// >>chng 12 apr 09, from 5.792 to 5.943, update backbround CR to Indiolo_07 (8x larger)
monitor column density CN   5.943 error 0.1
// >>chng 11 jul 16, from 10 to 12.77, add column density monitors
// >>chng 11 dec 12, from 12.77 to 12.72, bug-fix for updating grain opacity (r5759)
// >>chng 12 apr 09, from 12.72 to 12.67, update backbround CR to Indiolo_07 (8x larger)
monitor column density CH   12.67 error 0.1
//
// >>chng 05 jul 17, from 660 to 450 first run in 6 mo
// >>chng 08 dec 08, from 450 to 344, upper limit -> equals (r2515)
// >>chng 09 jan 16, from 344 to 345, average of 9 runs
// >>chng 12 jan 06, from 345 to 324, several H2 model changes
monitor nzone 324
//
// >>chng 04 dec 08, from 4 to 7 co-ion feedback, check converg
// >>chng 08 dec 08, from 7 to 3.52, upper limit -> equals (r2515)
// >>chng 08 dec 13, from 3.52 to 14.4, merging newsolvers branch
// >>chng 09 jan 16, from 14.4 to 14.29 (error 0.05), average of 9 runs
// >>chng 09 aug 02, from 14.4 to 14.0 (error 0.07), average of 3 runs
// >>chng 11 jun 14, from 14 to 12.23, new Te solver
// >>chng 11 jul 15, from 12.23 to 13.03 mean icc gcc cloud9
// >>chng 11 dec 12, from 13.03 to 11.92, bug-fix for updating grain opacity (r5759)
// >>chng 12 mar 07, from 11.92 to 9.877, renorm to r5961 results
// >>chng 12 apr 09, from 9.877 to 8.966, update backbround CR to Indiolo_07 (8x larger)
// >>chng 12 aug 16, from 8.966 to 9.535, fix radasc bug from r6346
// >>chng 12 aug 16, from 9.535 to 8.914, further fix of Rawlings H2 rates
monitor itrzn 8.914 error 0.07
//
// these were correct on 2004 dec 30, but command does not yet work
// >>chng 11 nov 16, from 21.26 to 21.19, adjust newmole monitors
// >>chng 12 apr 09, from 21.19 to 21.15, update backbround CR to Indiolo_07 (8x larger)
monitor H2 column density level 0  0  21.15 error 0.1
// >>chng 11 nov 16, from 20.62 to 20.41, adjust newmole monitors
// >>chng 12 oct 22, from 20.41 to 20.37, zone tau in rt_line_one
monitor H2 column density level 0  1  20.37 error 0.1
// 
// >>chng 05 sep 08 from 18.35 to 18.32, first run in some time
// >>chng 11 nov 16, from 18.32 to 13.89, adjust newmole monitors
// >>chng 12 jan 06, from 13.89 to 17.91, several H2 model changes
monitor H2 column density level 0  2  17.91 error 0.1
// 
// >>chng 05 sep 08 from 17.33 to 17.27, first run in some time
// >>chng 11 nov 16, from 17.27 to 14.19, adjust newmole monitors
// >>chng 12 jan 06, from 14.19 to 17.03, several H2 model changes
monitor H2 column density level 0  3  17.03 error 0.1
//
// >>chng 05 jul 17, from 16.21 to 16.14, first run in 6 mo
// >>chng 07 jan 10, from 16.14 to 16.10, H3+ to McCall rates
// >>chng 08 sep 25, from 16.1 to 16.06, remove damper on line pump (r2367)
// >>chng 11 nov 16, from 16.06 to 15.74, adjust newmole monitors
// >>chng 12 jan 06, from 15.74 to 15.84, several H2 model changes
// >>chng 12 apr 09, from 15.84 to 15.88, update backbround CR to Indiolo_07 (8x larger)
monitor H2 column density level 0  4  15.88 error 0.1
//
// >>chng 05 sep 08 from 15.84 to 15.80, first run in some time
// >>chng 11 nov 16, from 15.8 to 15.71, adjust newmole monitors
// >>chng 12 jan 06, from 15.71 to 15.62, several H2 model changes
monitor H2 column density level 0  5  15.62 error 0.1
// 
// >>chng 05 sep 08 from 14.85 to 14.79, first run in some time
// >>chng 11 nov 16, from 14.79 to 14.74, adjust newmole monitors
// >>chng 12 jan 06, from 14.74 to 14.67, several H2 model changes
monitor H2 column density level 0  6  14.67 error 0.1
// >>chng 12 jan 06, from 14.83 to 14.7, several H2 model changes
monitor H2 column density level 0  7  14.7 error 0.15
// >>chng 11 dec 12, from 13.98 to 14.02, bug-fix for updating grain opacity (r5759)
// >>chng 12 jan 06, from 14.02 to 13.92, several H2 model changes
monitor H2 column density level 0  8  13.92 error 0.1
// >>chng 12 jan 06, from 14.14 to 13.97, several H2 model changes
monitor H2 column density level 0  9  13.97 error 0.15
//
// >>chng 05 jul 17, from 13.45 to 13.37, first run in 6 mo
// >>chng 05 sep 08, from 13.37 to 13.31, first run in some time
// >>chng 08 aug 02, from 13.31 to 13.25 changes over past month
// >>chng 11 nov 16, from 13.25 to 12.87, adjust newmole monitors
// >>chng 12 jan 06, from 12.87 to 12.91, several H2 model changes
// >>chng 12 apr 09, from 12.91 to 12.96, update backbround CR to Indiolo_07 (8x larger)
monitor H2 column density level 1  0  12.96 error 0.1
//
// >>chng 05 sep 08, from 14.00 to 13.91, first run in some time
// >>chng 08 sep 25, from 13.91 to 13.87, remove damper on line pump (r2367)
// >>chng 11 nov 16, from 13.87 to 13.36, adjust newmole monitors
// >>chng 12 jan 06, from 13.36 to 13.51, several H2 model changes
monitor H2 column density level 1  1  13.51 error 0.1
//
// >>chng 05 jul 17, from 13.94 to 13.86, first run in 6 mo
// >>chng 05 sep 08, from 13.86 to 13.80, first run in some time
// >>chng 08 aug 02, from 13.80 to 13.74 changes over past month
// >>chng 11 nov 16, from 13.74 to 12.22, adjust newmole monitors
// >>chng 12 jan 06, from 12.22 to 13.39, several H2 model changes
// >>chng 12 apr 09, from 13.39 to 13.44, update backbround CR to Indiolo_07 (8x larger)
monitor H2 column density level 1  2  13.44 error 0.1
//
// >>chng 05 sep 08, from 14.07 to 13.97, first run in some time
// >>chng 11 nov 16, from 13.97 to 13.39, adjust newmole monitors
// >>chng 12 jan 06, from 13.39 to 13.59, several H2 model changes
monitor H2 column density level 1  3  13.59 error 0.1
//
c h2_HTT91.in

This is the Hollenbach et al 1991 Low-density PDR
The case b command appears because the Lyman lines are
vastly optically thick in this environment. 
If the command is removed the Lyman lines will be optically thin,
which will result in fast fluorescent excitation of the
(nearly totally neutral) hydrogen atom.  

there is very little CO in this model since it is not thick enough
for the UV pumping lines to become optically thick