#set term postscript enhanced eps color "Helvetica" 24
set term png truecolor enhanced font "Helvetica,36" size 1024,1024
set out "mb_T0.png"

# physics constants (in SI)
k = 1.38e-23
NA= 6.022e23
u = 0.001 / NA
T0 = 273.15

# Maxwell-Boltzmann distribution (mass in atomic units u, v in SI)
p(v,m,T) = 4. *pi * v**2. * (m*u/(2.*pi*k*T))**1.5 * exp( -m * u * v**2. / (2.*k*T))

# Formatting
set samples 10000
set key Left reverse at graph 0.9, 0.75
set yrange [0:.0022]
set xtics 1000 nomirror offset 0,0.25
set ytics nomirror 0.5e-3
set format y ""; set label 10 "10^{-3}" at -400,1.e-3
set border 3
set grid
set xlabel "v (m/s)" offset 13.5,2
set ylabel "p(v) (s/m)" offset 1, 5

set style fill transparent solid 0.4

# Plot for different gases at zero Celsius
set xrange [0:3900] 
set label 11 "T = 0 °C" at graph 0.35, 0.8
plot p(x,28,T0) t "N_{2} (m=28 u)" w filledcurve x1, \
     p(x,4,T0)  t "He (m=4 u)" w filledcurve x1, \
     p(x,2,T0)  t "H_{2} (m=2 u)"  w filledcurve x1