spectrum_BYTe.f90: Description of the input/output structure

Purpose: Program to generate synthetic synthetic spectra using the BYTe
         line list at specified temperatures. The spectrum is given either 
         as a stick diagram, or in the form of intensity profiles convoluted 
         with a Gaussian/Doppler profile on a grid of frequency points.
         The partition function value can be also recomputed, if it is not 
         provided by the user.

Input structure:
 
    ! number of Transition files to read
    !
    read*,nfiles
 
    ! names of Transition files 
    !
    do i = 1,nfiles
      read*,intfilename(i)
    enddo

    ! name of the Energy file
    !
    read*,enrfilename
 
    ! name of the swap-file to store the  entries of Transition files for the 
    selected frequency limits. 
    ! 'null' for no swapping. 
    !
    read*,swapfile

    ! number of irreps
    read*,nsym

    ! nuclear spin statistics weights
    !
     read*,(symlab(isym),gns(isym),isym=1,nsym)

    ! temperature (K), partition function; 
    ! if partfunc <0 the partition function will be computed using the energies
     provided
    !
    read*,temp,partfunc

    ! frequency range (cm-1) and number of grid points; the latter is not
    referenced for proftype='stick'
    !
    read*,freql,freqr,npoints

    ! form of spectra (profiles): 'gauss', 'doppler', or 'stick' 
    !
    read*,proftype
    !
    ! type of spectra:
    ! 'absorption': absorption coefficients (cm/mol) 
    ! 'emission': emission coefficients (Ergs/mol/Sr)
    ! 'partfunc': partition function for a series of temperatures together with
    derivatives
    !
    read*,specttype

    ! HWPar = HWHM (cm-1) if ProfType='gauss'
    ! HWPar = molecular mean molar mass (g) if ProfType='doppler'
    ! HWPar = a print our threshold for absorption coefficient (cm/mol) if 
    ProfType='stick'
    !
    read*, HWPar

    ! intensity cutoff (cm/mol or Ergs/mol/Sr) to spead up evaluation of 
    intensity, can be set negative for a zero-cutoff.
    ! not referenced for 'stick'
    !
    read*,thresh
    !

    !Output structure: 

    ! for 'gauss' and 'doppler'
    !
    print('(2(1x,es16.8))'), (Freq(i), Intens(i), i = 1, Npoints)
 
    ! for 'stick' the typical record  has the following format:

!     nu(cm-1)         I(cm/mol)   G_f   J_f    v1  v2  v3  v5    l3 l4 Gvib     K_f tau_f  E_f     <-  G_i  J_i    v1  v2  v3  v5    l3 l4 Gvib     K_i tau_i  E_i
   2.15512000E-01  2.52626561E-04  A2'   13     0   0   0   0     0   0 A2"      3   1    1752.7048 <- A2"   13     0   0   0   0     0   0 A1'      3   0    1752.4893

    ! where i,f stand for initial and final states, respectively;
    ! v1,v2,v3^l3,v4^l4 are the normal mode quantum numbers;
    ! G and G_vib are total and vibrational symmetries;
    ! E_i and E_f are the rovibrational term values;
    ! J,K,tau are the rotational quantum numbers: angular momentum, projection of 
    ! the angular momentum onto the z-axis, and rotational parity.