Molecular beam photoionization study of acetone and acetone-d/sub 6/
High resolution photoionization efficiency curves have been obtained for CH/sub 3/COCH/sub 3//sup +/ and CD/sub 3/COCD/sub 3//sup +/ using supersonic molecular beam sampling. As a result of adiabatic cooling during the nozzle expansion, sufficient concentrations of (CH/sub 3/COCH/sub 3/)/sub 2/, (CD/sub 3/COCD/sub 3/)/sub 2/, (CH/sub 3/COCH/sub 3/)/sub 3/, and (CH/sub 3/COCH/sub 3/)/sub 4/ were formed to permit the study of their photoion yield curves as well. Appearance potential curves have been determined for CH/sub 3/CO/sup +/, CD/sub 3/CO/sup +/, and (CH/sub 3/COCH/sub 3/) xCH/sub 3/CO/sup +/ fragments. The measured ionization potentials of acetone and acetone-d/sub 6/ monomers are 9.694 +- 0.006 and 9.695 +- 0.006 eV, respectively. Transitions to higher vibrational levels in CH/sub 3/COCH/sub 3//sup +/ are seen at 320, 695, and 930-1370 cm/sup -1/ above threshold. The effect of perdeutero substitution is to reduce these frequencies to 260 and 660--1100 cm/sup -1/. Appearance potentials of CH/sub 3/CO/sup +/ and CD/sub 3/CO/sup +/ fragments are observed at 10.52 +- 0.02 and 10.56 +- 0.02 eV, respectively. The measured ionization energies for (CH/sub 3/COCH/sub 3/)/sub n/, n=1--4, are found to decrease linearly as a function of 1/n. Observed ionization thresholds for (CH/sub 3/COCH/sub 3/)/sub 2/, (CH/sub 3/COCH/sub 3/)/sub 3/, and (CH/sub 3/COCH/sub 3/)/sub 4/ are 9.26 +- 0.03, 9.10 +- 0.03, and 9.02 +- 0.03 eV, respectively. Within experimental resolution, the ionization potentials of (CH/sub 3/COCH/sub 3/)/sub 2/ and (CD/sub 3/COCD/sub 3/)/sub 2/ are identical. The appearance potential of the process (CH/sub 3/COCH/sub 3/)/sub 2/ ..-->.. (CH/sub 3/COCH/sub 3/) xCH/sub 3/CO/sup +/+CH/sub 3/+e/sup -/ is found to be 10.08 +- 0.05 eV. By consideration of appropriate thermodynamic cycles, a lower bound for the acetone dimer ion binding energy is calculated to be 0.538 eV (12.4 kcal/mole) and the desolvation energy of (CH/sub 3/COCH/sub 3/) xCH/sub 3/CO/sup +/ is estimated to be 0.544 eV (12.5 kcal/mole).
- Research Organization:
- Department of Chemistry, University of New Mexico, Albuquerque, New Mexico 87131
- OSTI ID:
- 6638194
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 69:7
- Country of Publication:
- United States
- Language:
- English
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