Two-dimensional ( 2 + n ) resonance enhanced multiphoton ionization of HCl: State interactions and photorupture channels via low-energy triplet Rydberg states

Mass spectra were recorded for ( 2 + n ) resonance enhanced multiphoton ionization (REMPI) of HCl as a function of resonance excitation energy in the 81 710 - 82 870 cm − 1 region to obtain two-dimensional REMPI data. Small but significant fragmentations and H + , Cl + , as well as HCl + formations are found to occur after resonance excitations to the triplet Rydberg states f Δ 3 2 ( v ′ = 0 ) , f Δ 3 1 ( v ′ = 0 ) , and g Σ 3 + ( 1 ) ( v ′ = 0 ) . Whereas insignificant rotational line shifts could be observed, alterations in relative ion signal intensities, due to perturbations, clearly could be seen, making such data ideal for detecting and analyzing weak state interactions. Model analysis of relative ion signal intensities, taking account of the major ion formation channels following excitations to Rydberg states, its near-resonance interactions with ion-pair states as well as dissociations and/or photodissociations were performed. These allowed verification of the existence of all these major channels as well as quantifications of the relative weights of the channels and estimates of state interaction strengths. The proposed mechanisms were supported by ion signal power dependence studies.