Products of the ultraviolet photodissociation of trifluoroacetic acid and acrylic acid

Abstract

The photodissociation of trifluoroacetic and acrylic acids by the ultraviolet light from a flashlamp has been investigated by measuring the relative yields of some of the major products by time-resolved infrared absorption using tunable, narrow band diode lasers. Yields of CO₂ were measured both in the absence and presence of added O₂. The former experiments measure the CO₂ produced directly by decarboxylation of the acid, channel (2) below, the latter the sum of the yields from channels (1) and (2) since HOCO is rapidly converted to CO₂. The yields of CO from the decarbonylation channel (3) have also been measured. For trifluoroacetic acid, the relative yields are found to be [HOCO]:[CO₂]:[CO]=(0.28±0.07):(0.61±0.09):(0.11±0.06) and, for acrylic acid, [HOCO]:[CO₂]:[CO]=(0.32±0.08):(0.37±0.08):(0.31±0.09). The results are discussed in relation to the other, limited, measurements on the photodissociation of these acids and whether these three processes are likely to occur independently of one another.