;+
; NAME:
;  n2vp
; PURPOSE: (one line)
;  Return vapor pressure of N2 from Brown & Ziegler 1980
; CATEGORY:
;  Volatile Transport
; CALLING SEQUENCE:
;  vp = n2vp(t)
; INPUTS:
;  t : temperature, K
; KEYWORD INPUTS
;  None
; OUTPUTS:
;  vp : vapor pressure in microbar
; OPTIONAL OUTPUT
;  None
; RESTRICTIONS:
; PROCEDURE:
;  This function implements the tables of Brown and Zeigler 
; MODIFICATION HISTORY:
;  Written 2011 Aug 24, by Leslie Young, SwRI
;-
function n2vp, t

if isarray(t) then begin
   p = 0. * t
   for i = 0, n_elements(p)-1 do p[i] = n2vp(t[i])
   return, p
endif

; Return N2 vapor pressure, in microbar, as a function of temperature
a_liq  =[1.51050147e1, -6.15496072e2, -2.31314834e3, -5.89850934e4, 0.]
a_beta= [1.64302619e1, -6.50497257e2, -8.52432256e3,  1.55914234e5, -1.06368300e6]
a_alpha=[1.88550118d1, -8.57102332d2, -1.01891053d3,  1.28466570d4, -4.82177497d4]
a=a_beta
if t eq 0. then return, 0.
if t lt 35.62 then a=a_alpha
if t gt 63.152 then a=a_liq
p = exp( total((t^(-findgen(5))) * a))* 1.33322e3
return, p
end