; given molecule and isotope (HTRAN numbering), return the molecular weight
; For right now, specific to CO CSHELL project
function molec_weight, mol, iso

;+
; NAME:
;  molec_weight
; PURPOSE: (one line)
;  Return the molecular weight, given the molecule and isotope index used by HITRAN
; DESCRIPTION:
;  
; CATEGORY:
;  Spectra
; CALLING SEQUENCE:
;  w = molec_weight(mol, iso)
; INPUTS:
;  mol - molecule index (e.g., 1 for H2O)
;  iso - isotope index (e.g., 1 for 1H 16O 1H)
; OPTIONAL INPUT PARAMETERS:
;  none
; KEYWORD INPUT PARAMETERS:
;  none
; KEYWORD OUTPUT PARAMETERS:
;  none
; OUTPUTS:
;  atomic weight (g/mole, e.g., 18. for molec_weight(1,1) )
; COMMON BLOCKS:
;  None
; SIDE EFFECTS:
; RESTRICTIONS:
;  None
; PROCEDURE:
; MODIFICATION HISTORY:
;  Written 2000 October, by Leslie Young, SwRI
;-

H  = 1
C  = 6
N  = 7
O  = 8
F  = 9
P  = 15
S  = 16
Cl = 17
Br = 35
I = 53


case mol of 
; H2O    4  161  181  171  162
  1: case iso of 
        1: return,  atomic_weight(H,1) + atomic_weight(O,16) + atomic_weight(H,1)
        2: return,  atomic_weight(H,1) + atomic_weight(O,18) + atomic_weight(H,1)
        3: return,  atomic_weight(H,1) + atomic_weight(O,17) + atomic_weight(H,1)
        4: return,  atomic_weight(H,1) + atomic_weight(O,16) + atomic_weight(H,2)
     endcase
; CO2    8  626  636  628  627  638  637  828  728
  2: case iso of 
        1: return,  atomic_weight(O,16) + atomic_weight(C,12) + atomic_weight(O,16)
        2: return,  atomic_weight(O,16) + atomic_weight(C,13) + atomic_weight(O,16)
        3: return,  atomic_weight(O,16) + atomic_weight(C,12) + atomic_weight(O,18)
        4: return,  atomic_weight(O,16) + atomic_weight(C,12) + atomic_weight(O,17)
        5: return,  atomic_weight(O,16) + atomic_weight(C,13) + atomic_weight(O,18)
        6: return,  atomic_weight(O,16) + atomic_weight(C,14) + atomic_weight(O,17)
        7: return,  atomic_weight(O,18) + atomic_weight(C,12) + atomic_weight(O,18)
        8: return,  atomic_weight(O,17) + atomic_weight(C,12) + atomic_weight(O,18)
     endcase
; O3     5  666  668  686  667  676
  3: case iso of 
        1: return,  atomic_weight(O,16) + atomic_weight(O,16) + atomic_weight(O,16)
        2: return,  atomic_weight(O,16) + atomic_weight(O,16) + atomic_weight(O,18)
        3: return,  atomic_weight(O,16) + atomic_weight(O,18) + atomic_weight(O,16)
        4: return,  atomic_weight(O,16) + atomic_weight(O,16) + atomic_weight(O,17)
        5: return,  atomic_weight(O,16) + atomic_weight(O,17) + atomic_weight(O,16)
     endcase
; N2O    5  446  456  546  448  447
  4: case iso of 
        1: return,  atomic_weight(N,14) + atomic_weight(N,14) + atomic_weight(O,16)
        2: return,  atomic_weight(N,14) + atomic_weight(N,15) + atomic_weight(O,16)
        3: return,  atomic_weight(N,15) + atomic_weight(N,14) + atomic_weight(O,16)
        4: return,  atomic_weight(N,14) + atomic_weight(N,14) + atomic_weight(O,18)
        5: return,  atomic_weight(N,14) + atomic_weight(N,14) + atomic_weight(O,17)
     endcase
; CO     6   26   36   28   27   38   37
  5: case iso of 
        1: return,  atomic_weight(C,12) + atomic_weight(O,16)
        2: return,  atomic_weight(C,13) + atomic_weight(O,16)
        3: return,  atomic_weight(C,12) + atomic_weight(O,18)
        4: return,  atomic_weight(C,12) + atomic_weight(O,17)
        5: return,  atomic_weight(C,13) + atomic_weight(O,18)
        6: return,  atomic_weight(C,13) + atomic_weight(O,17)
     endcase
; CH4    3  211  311  212  
  6: case iso of 
        1: return,  atomic_weight(C,12) + 4*atomic_weight(H,1)
        2: return,  atomic_weight(C,13) + 4*atomic_weight(H,1)
        3: return,  atomic_weight(C,12) + 3*atomic_weight(H,1) + atomic_weight(H,2)
     endcase
; O2     3   66   68   67 
  7: case iso of 
        1: return,  atomic_weight(O,16) + atomic_weight(O,16)
        2: return,  atomic_weight(O,16) + atomic_weight(O,18)
        3: return,  atomic_weight(O,16) + atomic_weight(O,17)
     endcase
; NO     3   46   56   48
  8: case iso of 
        1: return,  atomic_weight(N,14) + atomic_weight(O,16)
        2: return,  atomic_weight(N,15) + atomic_weight(O,16)
        3: return,  atomic_weight(N,14) + atomic_weight(O,18)
     endcase
; SO2    2  626  646
  9: case iso of 
        1: return,  atomic_weight(O,16) + atomic_weight(S,32) + atomic_weight(O,16)
        2: return,  atomic_weight(O,16) + atomic_weight(S,34) + atomic_weight(O,16)
     endcase
; NO2    1  646  
 10: case iso of 
        1: return,  atomic_weight(O,16) + atomic_weight(N,14) + atomic_weight(O,16)
     endcase
; NH3    2 4111 5111
 11: case iso of 
        1: return,  atomic_weight(N,14) + 3*atomic_weight(H,1)
        2: return,  atomic_weight(N,15) + 3*atomic_weight(H,1)
     endcase
; HNO3   1  146
 12: case iso of 
        1: return,  atomic_weight(H,1) + atomic_weight(N,14) + 3*atomic_weight(O,16)
     endcase
; OH     3   61   81   62
 13: case iso of 
        1: return,  atomic_weight(O,16) + atomic_weight(H,1)
        2: return,  atomic_weight(O,18) + atomic_weight(H,1)
        3: return,  atomic_weight(O,16) + atomic_weight(H,2)
     endcase
; HF     1   19
 14: case iso of 
        1: return,  atomic_weight(H,1) + atomic_weight(F,19)
     endcase
; HCl    2   15   17
 15: case iso of 
        1: return,  atomic_weight(H,1) + atomic_weight(Cl,35)
        2: return,  atomic_weight(H,1) + atomic_weight(Cl,37)
     endcase
; HBr    2   19   11
 16: case iso of 
        1: return,  atomic_weight(H,1) + atomic_weight(Br,79)
        2: return,  atomic_weight(H,1) + atomic_weight(Br,81)
     endcase
; HI     1   17
 17: case iso of 
        1: return,  atomic_weight(H,1) + atomic_weight(I, 127)
     endcase
; ClO    2   56   76
 18: case iso of 
        1: return,  atomic_weight(Cl,35) + atomic_weight(O,16)
        2: return,  atomic_weight(Cl,37) + atomic_weight(O,16)
     endcase
; OCS    4  622  624  632  822
 19: case iso of 
        1: return,  atomic_weight(O,16) + atomic_weight(C,12) + atomic_weight(S,32)
        2: return,  atomic_weight(O,16) + atomic_weight(C,12) + atomic_weight(S,34)
        3: return,  atomic_weight(O,16) + atomic_weight(C,13) + atomic_weight(S,32)
        4: return,  atomic_weight(O,18) + atomic_weight(C,12) + atomic_weight(S,32)
     endcase
; H2CO   3  126  136  128
 20: case iso of 
        1: return,  2*atomic_weight(H,1) + atomic_weight(C,12) + atomic_weight(O,16)
        2: return,  2*atomic_weight(H,1) + atomic_weight(C,13) + atomic_weight(O,16)
        3: return,  2*atomic_weight(H,1) + atomic_weight(C,12) + atomic_weight(O,18)
     endcase
; HOCl   2  165  167
 21: case iso of 
        1: return,  atomic_weight(H,1) + atomic_weight(O,16) + atomic_weight(Cl,35)
        2: return,  atomic_weight(H,1) + atomic_weight(O,16) + atomic_weight(Cl,37)
     endcase
; N2     1   44
 22: case iso of 
        1: return,  2*atomic_weight(N,14)
     endcase
; HCN    3  124  134  125
 23: case iso of 
        1: return,  atomic_weight(H,1) + atomic_weight(C,12) + atomic_weight(N,14)
        2: return,  atomic_weight(H,1) + atomic_weight(C,13) + atomic_weight(N,14)
        3: return,  atomic_weight(H,1) + atomic_weight(C,12) + atomic_weight(N,15)
     endcase
; CH3Cl  2  215  217
 24: case iso of 
        1: return,  atomic_weight(C,12) + 3*atomic_weight(H,1) + atomic_weight(Cl,35)
        2: return,  atomic_weight(C,12) + 3*atomic_weight(H,1) + atomic_weight(Cl,37)
     endcase
; H2O2   1 1661
 25: case iso of 
        1: return,  2*(atomic_weight(H,1) + atomic_weight(O,16))
     endcase
; C2H2   2 1221 1231
 26: case iso of 
        1: return,  2*atomic_weight(H,1) + 2*atomic_weight(C,12)
        2: return,  2*atomic_weight(H,1) + atomic_weight(C,12) + atomic_weight(C,13)
     endcase
; C2H6   1 1221
 27: case iso of 
        1: return,  6*atomic_weight(H,1) + 2*atomic_weight(C,12)
     endcase
; PH3    1 1111
 28: case iso of 
        1: return,  3*atomic_weight(H,1) + 2*atomic_weight(P,31)
     endcase
; COF2   1  269
 29: case iso of 
        1: return,  atomic_weight(C,12) + atomic_weight(O,6) + 2 * atomic_weight(F,19)
     endcase
; SF6    1   29
 30: case iso of 
        1: return,  atomic_weight(S,32) + 6 * atomic_weight(F,19)
     endcase
; H2S    3  121  141  131
 31: case iso of 
        1: return,  atomic_weight(S,32) + 2 * atomic_weight(H,1)
        2: return,  atomic_weight(S,34) + 2 * atomic_weight(H,1)
        3: return,  atomic_weight(S,33) + 2 * atomic_weight(H,1)
     endcase
; HCOOH  1  126
 32: case iso of 
        1: return,  2 * atomic_weight(H,1) + atomic_weight(C,12) + 2 * atomic_weight(O,16)
     endcase
; HO2    1  166
 33: case iso of 
        1: return,  atomic_weight(H,1) + 2 * atomic_weight(O,16)
     endcase
; O      1    6 
 34: case iso of 
        1: return,  atomic_weight(O,16)
     endcase
; ClONO2 2 5646 7646, 
 35: case iso of 
        1: return,  atomic_weight(Cl,35) + 3*atomic_weight(O,16) + atomic_weight(N,14)
        2: return,  atomic_weight(Cl,37) + 3*atomic_weight(O,16) + atomic_weight(N,14)
     endcase
; NO+    1   46
 36: case iso of 
        1: return,  atomic_weight(N,14) + atomic_weight(O,16)
     endcase
endcase

end