Rsc_cp_c3cp54696a 3..14

Photodissociation of singlet oxygen, O2 a Dg, by ultraviolet radiation in the region from 200 to 240 nm has been investigated using velocity map imaging of the atomic oxygen photofragments. Singlet oxygen molecules are generated in a pulsed discharge and studied by one-laser photodissociation and detection around 226 nm as well as two color photodissociation at various wavelengths in the range from 200 to 240 nm. A simple model of the discharge on and off signal indicates efficient conversion of O2 X Sg (v = 0) in the parent beam to O2 a Dg(v = 0–2). Minute amounts of highly excited vibrational levels of ground state O2 X Sg (v > 0) are detected but no evidence is found for production of the O2 bSg + state. Over the decreasing wavelength range 240–200 nm the aDg-state signal relative to the XSg (v = 0) signal decreases strongly. Around 226 nm the aDg(v = 0–2) states averaged branching ratio percentage for O(Pj j = 2 : 1 : 0) is found to be 56 : 36 : 8 ( 5%), respectively. The anisotropy parameter for photodissociation of aDg(v = 0–2) averages to b = 1.3 0.4. The aDg(v = 0) photodissociation cross section is found to 3–10 times stronger than theory predicts. Furthermore, the photodissociation image shows a strong parallel character, (i.e., transition moment parallel to the molecular axis) while theory predicts a predominantly negative character.