Infrared spectra of trans-HOCO, HCOOH[sup +], and HCO[sub 2][sup −] trapped in solid neon

When a Ne:HCOOH sample is codeposited at ca. 5 K with neon atoms that have been passed through a microwave discharge, new absorptions appear in the infrared spectrum of the resulting solid that can be assigned to trans-HOCO, trans-HCOOH+, and HCO2−. The absorptions of trans-HOCO are readily identified by a comparison with those previously reported for that molecule trapped in solid argon. Preliminary assignments of infrared absorptions of HOCO+, confirmed in studies using another experimental system, are also suggested. The identifications of trans-HCOOH+ and of HCO2− are aided by study of the photodestruction characteristics of these products when the deposit is exposed to various wavelengths of visible and ultraviolet radiation, by an analysis of the spectra obtained from isotopically substituted samples, and by a comparison with the results of ab initio and density functional calculations. Three previously unidentified vibrational fundamentals of trans-HCOOH+ have been assigned, as have been four vibrational fundamentals of HCO2−, in the inert, nonionic environment of solid neon. The CH-stretching fundamental of HCO2− appears at an exceptionally low frequency. The results of density functional calculations of the structures and vibrational fundamentals of trans-HCOOH+, HCO2−, the W(C2v) structure of C(OH)2+, and cis- and trans-HCOOH− are given