Tunnel ionization of simple molecules by an intense CO2laser

Experiments have been performed investigating the interaction of an intense CO2 laser pulse of nanosecond duration with diatomic molecules O2, CO and NO as well as triatomic CO2. New measurements relating to the tunnel ionization behaviour of noble gas atoms have been performed. These results contain less data scatter than previous work and thus provide a useful reference with which to compare the molecular results. Comparison with theory shows that in the absence of vibrational resonance with the CO2 laser (in the weak field approximation), these 'simple' molecules are tunnel ionized as if they were structureless atoms with an ionization potential equivalent to that of the molecular ground state.