Infrared absorption of t-HOCO+, H+(CO2)(2), and HCO2- produced in electron bombardment of CO2 in solid para-H-2

Abstract

We have employed electron bombardment during matrix deposition of CO2 (or (CO2)-C-13, (CO2)-O-18) and para-hydrogen (p-H-2) at 3.2 K and recorded infrared (IR) spectra of t-HOCO+, H+(CO2)(2) , HCO2-, CO2-, t-HOCO, and other species isolated in solid p-H-2. After the matrix was maintained in darkness for 13 h, intensities of absorption features of t-HOCO+ at 2403.5 (v(1)), 2369.9 (v(2)), 1018.1 (v(4)), and 606.5 (v(6)) cm(-1) and those of H+(CO2)(2) at 1341.1, 883.6, and 591.5 cm(-1) decreased. Corresponding lines of isotopologues were observed when (CO2)-C-13 or (CO2)-O-18 replaced CO2. In contrast, lines of HCO2- at 2522.4 (v(1)), 1616.1 (v(5)), 1327.9 (v(2)), and 745.6 (v(3)) cm(-1) increased in intensity; corresponding lines of (HCO2-)-C-13 or (HCO2-)-O-18 were also observed. Lines of t-DOCO+ and DCO2- were observed in an electron bombarded CO2/normal-deuterium (n-D-2) matrix. Data of v(6) of t-HOCO+ and all observed modes of (HOCO+)-O-18-O-18 and (HCO2-)-O-18 are new. The assignments were made according to expected chemical behavior, observed isotopic shifts, and comparisons with vibrational wavenumbers and relative intensities of previous reports and calculations with the B3PW91/aug-cc-pVQZ method. The v(1) line of t-HOCO+ in solid p-H-2 (2403.5 cm(-1)), similar to the line at 2673 cm(-1) of t-HOCO+ tagged with an Ar atom, is significantly red-shifted from that reported for gaseous t-HOCO+ (3375.37 cm(-1)) due to partial proton sharing between CO2 and H-2 or Ar. The v(1) line of HCO2- in solid p-H-2 (2522.4 cm(-1)) is blue shifted from that reported for HCO2- in solid Ne (2455.7 cm(-1)) and that of HCO2- tagged with Ar (2449 cm(-1)); this can be explained by the varied solvation effects by Ne, Ar, or H-2 on the mixing of H+ + CO2 and H+ CO2- surfaces. Possible formation mechanisms of t-HOCO+, H+(CO2)(2), HCO2-, CO2-, t-HOCO, H2O, and t-HCOOH are discussed. Published by AIP Publishing.