;+
; NAME:
;  rt_reducedmass
; PURPOSE: (one line)
;  Return the reduced mass of two molecules
; DESCRIPTION:
;  Return the reduced mass of two molecules
; CATEGORY:
;  RT
; CALLING SEQUENCE:
;  eps = rt_vtefficiency(t, n, a10, p10, moldiam, molwgt)
; INPUTS:
;  molwgt1 - molecular weight of first molecule
;  molwgt2 - molecular weight of 2nd molecule
; OPTIONAL INPUT PARAMETERS:
;  none
; KEYWORD INPUT PARAMETERS:
;  none
; KEYWORD OUTPUT PARAMETERS:
;  none
; OUTPUTS:
;  collision rate/deexcitation rate
; COMMON BLOCKS:
;  None
; SIDE EFFECTS:
; RESTRICTIONS:
;  None
; PROCEDURE:
; 
;  Simple formular for reduced mass.  Could be extended with
;  Yelle 1991. "Non-LTE models of Titan's upper atmosphere,"
;  ApJ 383, 380-400, eqn 18.
; 
; MODIFICATION HISTORY:
;  Written 2004 Mar 17, Leslie Young SwRI
;  based on line 177 of mesopause.f, written by Roger Yelle, 1990
;-

function rt_reducedmass, molwgt1, molwgt2

;physconstants

invmu = 1./molwgt1 + 1./molwgt2

return, 1/invmu

end