ROTLIN_S Documentation (26/3/12)

ROTLIN_S is an extension of the original ROTLIN code developed by Alexander Faure. Originally it only calculated the rotational cross-sections using the T-matrices output from the R-Matrix codes, now the spin-coupling has been implemented (using the Infinite order sudden aprroximation in keeping with the original ROTLIN).

*NOTE THIS PROGRAM IS ONLY SUITABLE FOR LINEAR MOLECULES WITH SIGMA GROUND STATES* 

Information on the formulation in the original ROTLIN can be found in Section 2.2 of Rabadan et.al., J. Phys. B, 31 (1998), 2077-2090
Information on the formulation of the spin-coupling implementation can be found in section 4 of Corey & McCourt, J. Phys. Chem., 87 (1983), 2723-2730.

Firstly the T-matrices must be prepared by running them through the TMATSUB module. This changes the symmetry from C2_v back to the irreducible Cinf_v (Note: TMATSUB has currently only been tested to work correctly for molecules in the A1 ground state).

Both the pure rotational and spin-coupled rotational cross-sections can be obtained using this code. To calculate the pure rotational cross-sections simply do not specify values for trgspin, j, and jp.

*** Example ***
Within the test directory is some example jobfiles for a CN calculation, both for a pure rotational 0-1, and for a spin coupled 0-1 (j=1/2, j'=1/2). Both calculations have singlet and triplet parts. And post-calculation these should be summed with a (1/4 and 3/4 weighting respectively) to make the final cross-section.

IMPORTANT: If transition has Delta_N = 1, the Born correction can be applied using the cb_op=1 option. In this case you must look at fort.8 post-calculation to get the corrected cross-section.

INPUT VARIABLES (not all must be specified, please see example for general guide):

C***********************************************************************
C
C     Basic data is input via namelist /XSECIN/    
c      anr_op   = Switch to activate the ANR correction in the cross
c                 sections
c                 0= no correction, 1= correction applied (default)
c      be       = rotational constant (in cm-1)
c      cb_op    = Switch to activate the use of Coulomb-Born approx
c                 0= do NOT perform CB calculations (only T-matrix 
c                    cross sections)
c                 1= perform T-matrix plus CB calculations
c                 2= Only perform CB calculations (not T-matrices are
c                    required)
C      EMIN     = MINIMUM REQUIRED SCATTERING ENERGY (IN UNITS AS
C                 SPECIFIED BY IEUNIT)
C      EMAX     = MAXIMUM REQUIRED SCATTERING ENERGY
c      grid     = Kind of grid for energies when cb_op=2: 1=linear, 
c                 2=logarithmic
C      ITFORM   = 'F' if T-matrix dataset is formatted, else 'U'
C      IEUNIT   = UNITS of the output SCATTERING ENERGIES
C                 input ENERGIES are necessarily in Rydbergs 
C                 1= eV, 2= Hartree, 3= Ryd
c      IPRNT    = IPRNT(1)=1: print out all the input data. 
c                 IPRNT(4)=1,2,3,4: print out output data 
c                               (1 - short output, 4 -detailed output)     
C      IWRITE   = UNIT FOR console output
C      IXSN     = Units to be used for cross-section output
C                 2=ANGSTROM**2, 3=PI*BOHR**2
C      j	= j quantum number, only required for spin-rotation xsecs
C                 where j = |N-trgspin| -> N+trgspin
C      jp	= j' quantum number, only required for spin-rotation xsecs
C                 where jp = |Np-trgspin| -> Np+trgspin
c      ixsout   = Logical unit for cross sections output 
c      luchanv  = vector containing the logical units for channel input 
c                 files
c      lutmtv   = vector containing the logical units for t-matrix input
c                 files
C      MAXI     = LABEL OF HIGHEST INITIAL STATE FOR WHICH CROSS-
C                 SECTIONS ARE REQUIRED
C      MAXF     = LABEL OF HIGHEST FINAL STATE FOR WHICH CROSS-SECTIONS
C                 ARE REQUIRED
C      N        = INITIAL ROTATIONAL QUANTUM NUMBER
C      NP	= FINAL ROTATIOANL QUANTUM NUMBER
C      NAME     = TITLE FOR ANY OUTPUT
C      NTSET    = SET NUMBER OF T-MATRIX INPUT
c      nsym     = Number of molecular symmetries to consider
C      numener  = Number of energies to be read (the T-matrix files may 
c                 have T-matrix for a number of energies and this allows 
c                 not to read all of them but just "numener".) 
c                 If numener<1 (default), all T-matrices will be read.
c      q1       = Permanent dipole of the target (in Debye)
c      lmax     = Maximum value of l (partial waves) to add in the 
c                 computation of the partial CB cross section.
c      lmaxq    = Number of partial waves to use in the computation of
c                 the total quadrupole CB cross section
c      q2       = Permanent quadrupole of the target (in atomic units)
c      trgspin = The spin value of the target molecule ONLY, only define
C		  this variable if you want spin-rotation xsecs
