Vibrational spectra of molecular ions isolated in solid neon. XV. Infraredspectroscopic evidence for NeHF+ and HFFH+

When a Ne: HF mixture is subjected to Penning ionization and/or photoioniza tion by neon atoms in their first excited states, between 16.6 and 16.85 eV , and the products are rapidly frozen at approximately 5 K, the infrared sp ectrum of the resulting deposit includes absorptions assigned to NeHF+ and HFFH+. Evidence is presented suggesting that neon-matrix shifts may be anom alously large for protonated molecules which are derived from species with proton affinities near or below 550 kJ/mol. The results of earlier ab initi o studies, as well as those of the present experimental and ab initio studi es, indicate that the NeHF+ complex is quite strongly bound. The nu(3) abso rptions of NeHF+ and NeDF+ and the nu(1) + nu(3) absorption of NeHF+ are te ntatively identified. An absorption at 3064.7 cm(-1) has isotopic substitut ion behavior appropriate for its assignment to HFFH+. Density functional ca lculations were performed in order to estimate the positions of the harmoni c vibrational fundamentals of HFFH+-d(n), and a more elaborate two-dimensio nal calculation on the HF-stretching potential surface was conducted in an attempt to take into account the large anharmonic contribution. Processes w hich occur on ultraviolet irradiation of the deposit are considered. (C) 19 99 American Institute of Physics. [S0021-9606(99)00711-4].