Spectroscopy and Two-photon Dissociation of Jet-Cooled Pyruvic Acid

The UV photodissociation of pyruvic acid (PA) is studied in molecular beams using time of flight (TOF) mass spectroscopy and time-sliced Velocity Map Imaging (VMI) following excitation to the first absorption band(S1←S0) at 330-380 nm. CH3CO, HOCO, CO, CH3, and H are detected as photodissociation products. The photofragment yield (PFY) spectrum of the H product is recorded at 350-380 nm in He and Ar carrier gases. The spectrum shows sharp vibrational features reflecting the significant rotational cooling achieved in the molecular beam. It matches well the broad features observed in the room temperature absorption spectrum, and indicates that the S1 state lives longer than a picosecond. The origin band of the S1←S0 transition is identified at 26,710 cm-1 , and progressions in the CH3 and C-C torsional modes are tentatively assigned. Kinetic energy release (KER) and angular distributions of CH3CO, HOCO, CO, CH3, and H fragments indicate that additional photon absorption from S1 to the S2/S3 states is facile...