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

Abstract

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 and is followed by rapid dissociation to the observed fragments. On the basis of the energetics of the different dissociation pathways and analyses of the observed KER distributions, three-body fragmentation processes are proposed as major contributors to the formation of the observed products.

Infrared spectroscopy of 2-oxo-octanoic acid in multiple phases

“…6,16 Its photochemical products, reaction rates, and reaction mechanisms have been determined. 3,4,[16][17][18][19][20][21][22][23][24][25][26][27] The effect of water on its conformer distribution has also been experimentally and computationally investigated and its effect on PA's chemistry reported. 1,[28][29][30][31][32][33] Oxoacids are also found in oceans and aerosol particles, and their aqueous phase photochemistry has been extensively investigated.…”

Chemistry and Photochemistry of Pyruvic Acid at the Air–Water Interface

“…For both sources, these results were consistent with previous studies, which have described the mechanisms of bulk aqueous PA in detail. [83][84][85]93,10492,94,99,102,113 While the observed products are the same for both light sources, the normalized ion intensities of the photoproducts are generally smaller in the LED photolysis than in the Xe lamp photolysis. The lower intensity of the photolysis source and the limited overlap between the LED output and PA absorbance spectrum results in a lower photolysis rate, but these factors do not seem to significantly alter the photoproducts observed and therefore the photochemical pathways of PA.…”

“…Previous studies of the gas- and aqueous-phase chemistry of PA are the foundation of this work. The chemistry of PA in the gas phase has been extensively studied. − Unlike most organics, oxidation of PA by • OH or HO 2 is slow, and therefore, its atmospheric fate is determined by the direct absorption of sunlight by PA and the subsequent photochemical reactions. , Gas-phase photolysis of PA occurs on the singlet manifold, mainly producing CO 2 and methylhydroxycarbene, which isomerizes to acetaldehyde. ,,, This process occurs with a quantum yield of 1 at low buffer gas pressures. ,,, …”

Kinetic Study of Gas-Phase Reactions of Pyruvic Acid with HO2

“…It can also be formed in the photolysis of methylglyoxal generated from the reaction of biogenic VOCs including monoterpenes and has been detected in biomass burning plumes. In the atmosphere, it is believed that the primarily loss mechanism of PA is due to photolysis. − The primary photolysis products are acetaldehyde and CO 2 , and the photolysis rates have been well studied. − In competition with photochemical loss of PA are the oxidation reactions, especially by radical species such as OH and HO 2 . The reaction rate with OH has been experimentally estimated to be slow, although only one observation has been reported .…”

“…Karton studied the HO 2 catalyzed tautomerization of vinyl alcohol that operates via a similar mechanism. For the PA case, we can imagine an H atom transferred from the acid group to the ketone oxygen (i.e., CH 3 (CO)­COOH → CH 3 COH­(CO)O which is quickly followed by decarboxylation to yield the carbene product CH 3 COH. − This decarboxylation reaction was previously studied by Takahashi et al as a unimolecular process activated by high overtone excitation. It will be interesting to see if the reaction barrier can be lowered using the concerted double H atom exchange process mediated by HO 2 .…”