The double resonance ionisation nozzle cooled spectroscopy technique (DRINCS) has been used to extend the existing vibrational constants for some ion-pair states of I₂ and IC1. Some new ion-pair states of IC1 have also been observed. Some ion-pair potential energy curves beyond the previously existing RKR potentials have been generated using only the vibrational Dunham coefficients and the known asymptotic behaviour of the Coulombic branch of the potentials of I₂. These potentials have been used to simulate the DRINCS spectra. The lifetime of the f'(v'=0) ion-pair state of I₂ has been determined as 142±6 ns. The electronic transition dipole moment function has been calculated by simulation of the dispersed fluorescence from the (v'=11) level of the f' ion-pair state. Numerical modelling techniques have been used to simulate the vibronic coupling between an ion-pair and Rydberg state of I₂. A theoretical study of some Rydberg and ion-pair electronic states of the H₂...HF cluster have been carried out using ab initio calculations. In addition, some states of the (H₂...HF)⁺ cation have been investigated.