Photochemistry of formic acid monomer at 222 nm

The yields of CO₂ and CO formed from the gas-phase photolysis at 222 nm of very low pressures of formic acid where the monomer predominates have been determined using FTIR spectroscopy. The observed ratio of CO₂/CO approaches unity as the formic acid pressure approaches zero. Previous studies have shown that the quantum yield for HCOOH + hv → OH + HCO (or H + CO) is 0.70 at 298 K. The present experimental results indicate that the ratio of the quantum yields of the possible molecular photolysis channels forming H₂ + CO₂ (?_1b) and H₂O + CO (?_1c) is ca. 1. Including this result in an analysis of previously reported quantum yields of CO and CO₂ determined at higher pressures of formic acid, where both monomer and dimer contribute significantly to the products, indicates that ?_1b = ?_1c = 0. © 1994 John Wiley & Sons, Inc.