Below follows a description of the format adopted for presenting the atomic and molecular data in LAMDA. Any similarities with datafiles from other authors is completely coincidental.

Lines 1 – 2: molecule (or atom) name
Lines 3 – 4: molecular (or atomic) weight (a.m.u.)
Lines 5 – 6: number of energy levels (NLEV)
Lines 7 – 7+NLEV: level number, level energy (cm-1), statistical weight. These numbers may be followed by additional info such as the quantum numbers, which are however not used by the program. The levels must be listed in order of increasing energy.
Lines 8+NLEV – 9+NLEV: number of radiative transitions (NLIN)
Lines 10+NLEV – 10+NLEV+NLIN: transition number, upper level, lower level, spontaneous decay rate (s-1). These numbers may be followed by additional info such as the line frequency, which is however not used by the program.
Lines 11+NLEV+NLIN – 12+NLEV+NLIN: number of collision partners (NPART)
This is followed by NPART blocks of collision data:
Lines 13+NLEV+NLIN – 14+NLEV+NLIN: collision partner ID and reference. Valid identifications are: 1=H2, 2=para-H2, 3=ortho-H2, 4=electrons, 5=H, 6=He, 7=H+.
Lines 15+NLEV+NLIN – 16+NLEV+NLIN: number of transitions for which collisional data exist (NCOL)
Lines 17+NLEV+NLIN – 18+NLEV+NLIN: number of temperatures for which collisional data are given
Lines 19+NLEV+NLIN – 20+NLEV+NLIN: the NTEMP values of the temperature for which collisional data are given
Lines 21+NLEV+NLIN – 21+NLEV+NLIN+NCOL: transition number, upper level, lower level; rate coefficients (cm³s^-1) at each temperature.
The treatment of collision data between these points and outside this range depends on the program. RADEX and RATRAN interpolate between rate coefficients in the specified temperature range. Outside this range, they assume that the collisional de-excitation rate coefficients are constant with T, i.e., they use rate coefficients specified at the highest T (400 K in this case) also for higher temperatures, and similarly at temperatures below the lowest value (10 K in this case) for which rate coefficients were specified.

Example molecular data file: HCO+

!MOLECULE
HCO+
!MOLECULAR WEIGHT
29.0
!NUMBER OF ENERGY LEVELS
21
!LEVEL + ENERGIES(cm^-1) + WEIGHT + J
1 0.000000000 1.0 0
2 2.975008479 3.0 1
(etc)
21 624.269300464 41.0 20
!NUMBER OF RADIATIVE TRANSITIONS
20
!TRANS + UP + LOW + EINSTEINA(s^-1) + FREQ(GHz)
1 2 1 4.251e-05 89.18839570
2 3 2 4.081e-04 178.37481404
(etc)
20 21 20 4.955e-01 1781.13802857
!NUMBER OF COLL PARTNERS
1
!COLLISIONS BETWEEN
1 H2-HCO+ from Flower (1999)
!NUMBER OF COLL TRANS
210
!NUMBER OF COLL TEMPS
12
!COLL TEMPS
10.0 20.0 30.0 50.0 70.0 100.0 150.0 200.0 250.0 300.0 350.0 400.0
!TRANS + UP + LOW + COLLRATES(cm³ s^-1)
1 2 1 2.6e-10 2.3e-10 2.1e-10 2.0e-10 1.9e-10 1.8e-10 2.0e-10 2.2e-10 2.3e-10 2.5e-10 2.7e-10 2.8e-10
2 3 1 1.4e-10 1.2e-10 1.1e-10 1.0e-10 9.2e-11 8.8e-11 8.4e-11 8.2e-11 8.1e-11 8.3e-11 8.1e-11 8.5e-11
(etc)
210 21 20 3.7e-10 3.6e-10 3.6e-10 3.5e-10 3.5e-10 3.5e-10 3.8e-10 4.0e-10 4.4e-10 4.7e-10 5.0e-10 5.2e-10