Extreme high rotational excitation of ClO

We observed the population of extremely high non-thermal rotational states of ClO (J max  = 130.5) upon photodissociation of Cl 2 O. State-resolved and isotope-specific detection of nascent ClO is performed by observing single colour (2 + 1) resonance enhanced multiphoton ionisation (REMPI) spectra following excitation in the wavelength range from 336 to 344 nm. The REMPI spectrum is assigned to the ClO(C 2 Σ – , v′ = 0 ← X 2 Π Ω , v = 0) transition. The non-thermal population of rotational states is highly inverted, peaking at J = 107.5. The photodissociation of Cl 2 O is a classical example for the pure impulsive model, as a consequence of the Cl 2 O mass distribution and a weak dependence of the upper potential energy surface on the bond angle. Cl 2 O can thus be used as clean source for laboratory generation of highly excited ClO molecules with a defined non-thermal rotational population. In kinetic studies using ClO from Cl 2 O as precursor the high rotational excitation needs to be considered carefully.