Photodissociation and photoionization cross sections

See photo.tar file with the photodissociation (.pd) and
photoionization (.pi) cross sections. The basic reference is:

E.F. van Dishoeck 1988, in Rate Coefficients in Astrochemistry, eds.
T.J. Millar and D.A. Williams (Kluwer), p. 49-72.

The format is:

- line 1:       title
- line 2:       number of discrete transitions N (5 in this case)
- line 3-3+N:   - label of transition
                - wavelength (A) 
                - pi e^2/m c^2  lambda^2 f eta (cm^2 A)  (See Eq. 2)

- line 3+N+1:   number of wavelengths M at which continuous cross section is
                specified
- line 3+N+2:   lower wavelength threshold for continuous cross section
                (cross section is zero for lambda < lambda_th)
                this is often indicated with a minus sign, or, in case
                the zero is explicitly listed as the last point, as -1.
- line 3+N+2+M: - label 
                - wavelength (A)
                - cross section (cm^2) at specific wavelengths
                  you need to make a spline fit through these points to get 
                  the continuous cross section as a function of wavelength 
                  (See Eq. 1)

Photoionization is only by continuous absorption.