Tunable Synchrotron Vacuum Ultraviolet Ionization, Time-of-Flight Investigation of the Photodissociation of trans-Crotonaldehyde at 193 nm

Abstract

Photodissociation of the unsaturated trans-crotonaldehyde (CH 3 CHCHCHO) molecule at 193 nm is studied using photofragment translational spectroscopy (PTS) and detected by ionization with tunable synchrotron ultraviolet radiation. The photofragment time-of-flight (TOF) spectra at mle = 68(C 4 H 4 O + ), 55(C 3 H 3 O + ), 41(C 3 H 5 + ), 40(C 3 H 4 + ), 39(C 3 H 3 + ), 29(?), 28(CO + ), 27(C 2 H 3 + ), 26(C 2 H 2 + ), and 15(CH 3 + ) are measured. Mass 29 could not be unambiguously assigned. Analysis of these experimental results reveals three dissociation channels: H + C 4 H 5 O, CH 3 + C 3 H 3 O, and CO + C 3 H 6 . A fourth channel associated with mass 29 could reflect either formation of HCO or C 2 H 5 . The measurements also indicate that C 3 H 6 undergoes strong secondary dissociation. The center of mass (CM) translational energy distributions obtained by fitting the TOF mass spectra of the fragments yield values 42, 23, and 43 kJ/mol average CM kinetic energies for the H + C 4 H 5 O, CH 3 + C 3 H 3 O and CO + C 3 H 6 channels, respectively. The photoionization yield curve of the CHCHCHO radical is measured for the first time with an onset ≤7.6 eV. The photodissociation mechanism of crotonaldehyde is compared with the photodissociation dynamics of acrolein (CH 2 CHCHO).