function dopwidth, nu0, t, mu

;+
; NAME:
;  dopwidth
; PURPOSE: (one line)
;  Calculate the doppler width of a spectral line
; DESCRIPTION:
;  The doppler width follows the Goody and Yung definition
; CATEGORY:
;  Spectra
; CALLING SEQUENCE:
;  dopw = dopwidth(nu0, t, mu)
; INPUTS:
;  nu0 - wavenumber of the line in cm^-1
;  t - temperature (K)
;  mu - molecular weight (g/mole)
; OPTIONAL INPUT PARAMETERS:
;  none
; KEYWORD INPUT PARAMETERS:
;  none
; KEYWORD OUTPUT PARAMETERS:
;  none
; OUTPUTS:
;  doppler width in cm^-1
; COMMON BLOCKS:
;  None
; SIDE EFFECTS:
; RESTRICTIONS:
;  Note that if nu0 is in other units (e.g. nm), the returned
;  width will be in those same units.
; PROCEDURE:
; MODIFICATION HISTORY:
;  Written 2000 October, by Leslie Young, SwRI
;-

  physconstants
  return, (nu0/!phys.c) * sqrt(2.*!phys.k*t/(mu*!phys.m_u))

end