Mid-infrared spectra of the proton-bound complexes Nen–HCO+ (n=1,2)

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Abstract
The ν1 band of Ne–HCO+ has been recorded for both 20Ne and 22Ne containing isotopomers by means of infrared photodissociationspectroscopy. The rotational structure of the band is consistent with a parallel Σ–Σ type transition of a linear proton‐bound complex. The following constants are extracted for 20Ne–HCO+: ν0=3046.120±0.006 cm−1, B″=0.099 54±0.000 05 cm−1, D″=(5.30±0.30)×10−7 cm−1, H″=(1.1±0.9)×10−11 cm−1, B′=0.100 03±0.000 05 cm−1, D′=(4.89±0.30)×10−7 cm−1, H′=(1.6±0.9)×10−11 cm−1. The ν1 band is redshifted by 42.5 cm−1 from the corresponding ν1 transition of free HCO+ indicating that the Ne atom has a pronounced influence on the proton motion. Linewidths for individual rovibrational transitions are laser bandwidth limited, demonstrating that the lifetime of the ν1 level is at least 250 ps. An approximate radial potential for the collinear Ne...HCO+ interaction is constructed by joining the mid‐range potential obtained from a Rydberg–Klein–Rees inversion of the spectroscopic data to the theoretical long‐range polarization potential. Based on this potential, the estimated dissociation energy (D 0) for Ne–HCO+ is 438 cm−1 in the (000) state and 454 cm−1 in the (100) excited state. The rotationally unresolved ν1 band of 20Ne2–HCO+ is slightly blueshifted with respect to that of 20Ne–HCO+. The observed frequency shift is compatible with a trimer structure where the second Ne atom is attached to the linear Ne–HCO+ dimer core.

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