Finding Potassium's ionisation potential using Sharp, Principal etc. Series

1. Feb 22, 2012

EmmaLemming

1. The problem statement, all variables and given/known data

Make a rough estimate of the ionisation potential of potassium (19) given the following infomation relating to its optical spectrum:

wavelength of the first line of the Sharp Series: 1248nm
wavelength of the first line of the Principal Series: 767nm
wavelength of the first line of the Diffuse Series: 1173nm
wavelength of the first line of the Fundamental series: 1516nm

speed of light = 2.998 x 10^8 m/s
Planck Constant = 6.626 x 10^(-34)
Rydberg constant R∞ = 1.097 x 10^7
electronic charge = -1.602 x 10^(-19)

2. Relevant equations

I = (Rhc)/((n-δ)^2)

3. The attempt at a solution

I have no idea how to go about this at all. I have tried but got nothing..

I was told that δ was a ratio of some sort.. but I don't know what of..

A method of how to go about this would be great and an explanation of why would be handy too.