### Fit Function: VERNER

 Fit Function \begin{align*} \sigma_{ph}(pt) = pcf(4) \times 10^{-18} \left[\left(y-1\right)^2+ \left(pcf(7)\right)^2\right]\left[y^{0.5pcf(5)-pcf(9)-5.5}\right] \\ \left[\left(1+\sqrt\frac{y}{pcf(6)}\right)^{-pcf(5)}\right]; y = \frac{pt}{pcf(3)} \end{align*} Comments

#### Fortran

Arguments
namedescriptionunitstype(s)
pt photon energy eV real, dimension(:)
pcf coefficient data array real, dimension(9)
kncf number of coefficients in the data array integer
pfit cross section cm2 real, dimension(:)
kermsg error message character
Return values
namedescriptionunitstype(s)
pfit cross section cm2 real, dimension(:)
Code
c
c###################################################################
c
subroutine verner(pt, pcf, kncf, pfit, kermsg)
c
c     At. Data. Nucl. Data Tables 55 2233 (1993)
c
c     this is a subroutine to calculate photoionization cross-sections
c     in cm[2] as function of photon energy in ev for an electron
c
c     sigma_{ph}(k) = S_0*F(y), y =k/k_0,                                 (1)
c     F(y) = [(y-1)^2+(y_w)^2][y^{0.5P-xl-5.5}][(1+sqrt(y/y_a))^{-P}]     (2)
c
c     pt = k         photon energy (eV)
c
c     pcf is the coefficient data array, where
c     pcf(1) =  E_{th}       Ionization threshold energy in eV
c     pcf(2) =  k_{max}      Maximum photon energy in eV to
which the fitting was performed
c     pcf(3) =  k_0          Fit parameter used in Eq.(1) in eV
c     pcf(4) =  S_0          Fit parameter used in Eq.(1) in Mb
c     pcf(5) =  P,           Dimensionless fit parameters used in Eq.(2)
c     pcf(6) =  y_a,         Dimensionless fit parameters used in Eq.(2)
c     pcf(7) =  y_w          Dimensionless fit parameters used in Eq.(2)
c     pcf(8) =  del          Relative root-mean-square error of fitting in percent
c     pcf(9) =  xl           Angular momentum quantum number

c     kermsg = blank if no errors
c
c     pfit = photo ionization cross-sections in cm[2]
c
c     written by H. K. Chung , iaea atomic and molecular data unit
c
c------------------------------------------------------------------------
c
double precision pt, pcf, pfit, q
dimension pcf(9)
character*(*) kermsg
data ry/13.58/
c
kermsg = ' '

eth=pcf(1)
xmax=pcf(2)
x0=pcf(3)
S0=pcf(4)
p=pcf(5)
ya=pcf(6)
yw=pcf(7)
del=pcf(8)
xl=pcf(9)
c

if(pt.le.eth)then
c         goto 900
pt=eth
endif

y=pt/x0
q=-(5.5+xl-0.5*p)
a1=y**q
a2=(y-1.)**2 + yw**2
a3=(1.+sqrt(y/ya))**(-p)
fy=a1*a2*a3
c
pfit = S0 * 1.e-18 * fy

return

c 900  pfit=1.e-30

return
c
end

#### Python

Arguments
namedescriptionunitstype(s)
pt photon energy eV float, np.ndarray
pcf coefficient data array float, np.ndarray
kncf number of coefficients in the data array int
pfit cross section cm2 float, np.ndarray
kermsg error message str
Return values
namedescriptionunitstype(s)
pfit cross section cm2 float, np.ndarray
Code