When the file N_pop.ijs is loaded into a J session, it will
read in all the ionic data found in the "ion_list=: 'C1';'C2' ..."
lines of the code. The ionic data should have the following 
format:

---------------------------------------
'name of level (string)' , statistical weight, energy in eV, integer index of level
 (for readability, blank lines (LF only!) may be included)

this section ends with "**********" (10 *'s, no blanks)

a list of the Einstein A coefficients, preceeded by the lower & upper level indices

section ends with "**********"

a list of the (temperature dependent) collision cross sections. the list is
preceeded by a line giving the temperatures for which the cross sections are
tabulated (in 10e-4 degrees K). The following lines give

(lower level) (upper level) (list of cross sections for each temperature)

section ends with "**********"

arbitrary comments may follow -- this material not read
----------------------------------------

Consider the O++ (O III) ion. Suppose we are interested in a temperature of
13,000 K and an electron density of N_e = 650 /cm^3. In the J session we enter

   'O3' pop 13000 650

0.107116 0.317339 0.517697   0.0568128 0.00089976 0.000135143 <- Boltzmann distribution
0.399473 0.460017 0.140456  5.36676e_5 7.14914e_9 1.17997e_11 <- the actual populations
 3.72936  1.44961 0.271309 0.000944639 7.94561e_6  8.73128e_8 <- (actual)/(Boltzmann)
       
If we want the radiation emitted under these conditions, we enter

   'O3' emiss 13000 650
          0           0           0           0 0 0
2.71497e_19           0           0           0 0 0
2.58511e_25 5.26653e_19           0           0 0 0
5.92126e_22 1.44839e_18 4.17154e_18           0 0 0
          0 1.36399e_20 4.77993e_23 5.79193e_20 0 0
	  0 2.99138e_20 7.34191e_20           0 0 0
	
The output is arranged as the transition matrix. To get a list of spectral lines:

   'O3' lines 13000 650
+-----------------+---+-----------------+-------+-----------+
|'2s 2p^3  5S0(2)'|-->|'2s^2 2p^2 3P(1)'|1661.16|2.99138e_20|
+-----------------+---+-----------------+-------+-----------+
|'2s 2p^3  5S0(2)'|-->|'2s^2 2p^2 3P(2)'|1666.52|7.34191e_20|
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 1S(0)'|-->|'2s^2 2p^2 3P(1)'|2321.06|1.36399e_20|
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 1S(0)'|-->|'2s^2 2p^2 1D(2)'|4363.14|5.79193e_20|
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 1D(2)'|-->|'2s^2 2p^2 3P(0)'|4931.71|5.92126e_22|
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 1D(2)'|-->|'2s^2 2p^2 3P(1)'|4959.46|1.44839e_18|
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 1D(2)'|-->|'2s^2 2p^2 3P(2)'|5007.5 |4.17154e_18|
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 3P(2)'|-->|'2s^2 2p^2 3P(1)'|51.6914|5.26653e_19|
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 3P(1)'|-->|'2s^2 2p^2 3P(0)'|88.1582|2.71497e_19|
+-----------------+---+-----------------+-------+-----------+

This boxed table gives the upper level, the lower level, the wavelength
of the line in Angstroms (or microns if greater than 10,000A), and the
energy emitted in ergs/s/cm^3/ion.

Certain line ratios are important, e.g. 5007/4363. This ratio is given by

   O3r 13000 650
72.0233

The total energy radiated by the ion in all transitions is obtained
by summing (+/+/) the emission matrix:

   'O3' Rad_Loss 13000 650
1.0144e_20

This result has been divided by the electron density (N_e), as this
varies less strongly under change of N_e.

Another example, the Ne V ion:

   'Ne5' lines 15000 3e5
+-----------------+---+-----------------+-------+-----------+
|'2s 2p^3  5S0(2)'|-->|'2s^2 2p^2 3P(1)'|1130.86|3.43483e_18|
+-----------------+---+-----------------+-------+-----------+
|'2s 2p^3  5S0(2)'|-->|'2s^2 2p^2 3P(2)'|1139.86|8.7134e_18 |
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 1S(0)'|-->|'2s^2 2p^2 3P(1)'|1575.15|1.0658e_17 |
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 1S(0)'|-->|'2s^2 2p^2 1D(2)'|2974.75|3.81924e_18|
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 1D(2)'|-->|'2s^2 2p^2 3P(0)'|3299.99|8.20917e_20|
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 1D(2)'|-->|'2s^2 2p^2 3P(1)'|3345.71|4.47555e_16|
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 1D(2)'|-->|'2s^2 2p^2 3P(2)'|3425.74|1.21787e_15|
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 3P(2)'|-->|'2s^2 2p^2 3P(1)'|14.3225|3.15923e_16|
+-----------------+---+-----------------+-------+-----------+
|'2s^2 2p^2 3P(1)'|-->|'2s^2 2p^2 3P(0)'|24.1479|3.94376e_17|
+-----------------+---+-----------------+-------+-----------+