Organic molecules energy levels

The emitted P particles excite the organic molecules which, in returning to normal energy levels, emit light pulses that are detected by a photomultiplier tube, amplified, and electronically counted. Liquid scintillation counting is by far the most widely used technique in tritium tracer studies and has superseded most other analytical techniques for general use (70). 

Figure 6.1 Orbital energy-level diagram for a typical organic molecule...

Useful books from the Oxford University Press primer series include Foundations of Spectroscopy, by Simon Duckett and Bruce Gilbert, OUP, Oxford, 2000 Introduction to Organic Spectroscopy, by Laurence M. Harwood and Timothy D. W. Claridge, OUP, Oxford, 1997 and Energy Levels in Atoms and Molecules, by W. G. Richards OUP, Oxford, 1996. Each, particularly the last, represents a clear and lucid introduction. 

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