The Infrared Spectra of the NH3-dn+ Cations Trapped in Solid Neon
Warren E. Thompson, Marilyn E. Jacox
When a dilute mixture of NH3 in neon is subjected to Penning ionization and/or photoionization by neon atoms in their first excited states, between 16.6 eV and 16.85 eV, and the products are rapidly frozen at approximately 5 K, the infrared spectrum of the resulting deposit includes three relatively prominent product absorptions which agree well with the positions determined in earlier gas-phase studies for the three infrared-active fundamentals of 14NH3+. The corresponding fundamentals of 15NH3+, 14ND3+, and 15ND3+ have been observed as have been many of the fundamentals of the partially deuterium-substituted cations, in experiments on isotopically enriched NH3 samples. When the effects of anharmonicity are considered (including the occurrence of negative anharmonicity for the out-of-plane deformation fundamental), the positions of these absorptions agree satisfactorily with those predicted in an earlier study from the fit of an ab initio potential surface to the experimental data for 14NH3+, as well as with those predicted in the present study from a least-squares force constant adjustment to the frequencies observed for the various isotopomers.