Low-energy electron-energy-loss spectroscopy of condensed acetone: Electronic transitions and resonance-enhanced vibrational excitations

Abstract

We report electron-energy-loss spectroscopy, within the incident electron energy range 1 to 19 eV, of solid films of acetone condensed at 18 K. The strong Rydberg progressions, which usually dominate the spectra in the gas phase, are found to completely disappear in the solid phase. In the absence of these transitions, the remaining broad bands centered at 4.3, 4.5, 6.2, 8.7, and 9.8 eV energy loss can be assigned to the 1 3A2(n→π*), 1 1A2(n→π*), 1 3A1(π→π*), 1 3B1(σ→π*), and 2 3A2(σ→π*) valence electronic transition of acetone, respectively. A broad feature ranging from 11 to 16 eV and having a maximum around 13.8 eV is ascribed to several overlapping autoionizing excited states. From a comparison with infrared and Raman spectra, the energy-loss peaks observed below 1 eV are found to be due to excitation of the fundamental, overtone, and combination vibrational modes of the molecule. Their incident energy dependence is showing broad vibrational enhancement maxima at 4, 7, and 9 eV, which are attributed to the formation of single-particle or shape resonances of 2B1, 2A1, and 2A2 (or 2B2) symmetries, respectively.

The VUV electronic spectroscopy of acetone studied by synchrotron radiation

“…The LUMO arises from the 3b 1 p * CO anti-bonding orbital, whereas the second unoccupied molecular orbital 9a 1 shows an in-phase combination of two p * CH anti-bonding orbital localized on the methyl groups. 30 According to the (2 + 1 0 ) REMPI studies of Wiedman et al, 31 the lowest adiabatic ionisation energy is 9.708 eV.…”

“…The 5b 2 highest occupied molecular orbital has been identified as representing the oxygen 2p y non-bonding electrons with a slightly anti-bonding character similar to a p * CO orbital in the molecular plane and a considerable bonding character between the CO and the CH 3 groups. 30 The second highest occupied molecular orbital, 2b 1 , is of CO p-bonding character. The LUMO arises from the 3b 1 p * CO anti-bonding orbital, whereas the second unoccupied molecular orbital 9a 1 shows an in-phase combination of two p * CH anti-bonding orbital localized on the methyl groups.…”

Final State Distributions of Methyl Photoproducts from the Photooxidation of Acetone on TiO2(110)

“…Of particular interest are “anion” excited states which are formed by electron transfer at the titania interface that could result in dissociation of adsorbates, i.e., dissociative electron attachment (DEA). On metal surfaces, “hot” electron transfer or DEA is the dominant process for substrate induced photochemistry of adsorbed molecules, in large part because the corresponding holes are effectively shielded by the metal valence electrons. , In the gas phase, the small ketones (acetaldehyde, formaldehyde, acetone) − and carboxylic acids (acetic acid, propionic acid) , exhibit negative ion resonances associated with electron scattering in the range of 1–1.5 eV, which lead to vibrational excitation in the case of acetone, whereas acetic acid undergoes DEA into various fragments including CH 2 and CH 3 . Acetone DEA is only observed for electron attachment resonances that lie above ∼7 eV .…”

Photoabsorption spectroscopy of dimethyl sulfoxide at the O1s, C1s, S2s, and S2p Regions: A comparison with acetone

“…Experimental and theoretical studies of electronic structure of the ground and excited states, as well as the electronic transition probabilities for the valence and the inner shell electrons for both DMSO and acetone, have been done in the past 40 years. These molecules have been excited at the valence7–14 and inner shell regions,8, 15–21 using synchrotron radiation and electron energy loss, or laser spectrometers. Theoretical studies have been done for both DMSO1, 3, 22–24 and acetone,25–29 in the valence region, mainly using configuration interaction methods.…”