Electron-impact spectroscopy of acetaldehyde

Abstract

Acetaldehyde has been studied by the technique of low-energy variable-angle electron energyloss spectroscopy. With this method the low-lying spin-forbidden transitions have been located via the behavior of the relative differential cross sections, providing the first identification by this technique of such states in acetaldehyde. High-lying states were also investigated and some assignments of dipole symmetry-forbidden/quadrupole symmetry-allowed excitations were made on the basis of characteristic angular behavior, evident for the asymmetric molecule acetaldehyde just as for the symmetric molecules formaldehyde and acetone. Through a comparison of the acetaldehyde results with those for formaldehyde and acetone the trends in the allowed and forbidden transition energies were examined as a function of methyl substitution and found to be relatively linear.

Low-energy elastic electron scattering by acetaldehyde

“…Measured cross sections for vibrational excitation by electron impact have shown both the π * resonance [10,11], at about 1.2 eV, and a further broad peak at 6.8 eV, assigned to one or more σ * resonances [10]. Other measurements have determined thresholds and, in some cases, relative cross sections for electronic excitation [8,10,[12][13][14][15][16], while still others have examined dissociative electron attachment [10,[17][18][19] and electron-impact ionization [20][21][22]. Burean and Swiderek [23] have studied the chemistry induced in condensed acetaldehyde by low-energy electron impact.…”

Vibronic coupling in excited states of acetone

“…7 Concentrating on the singlet manifold, we see that excitation from this lone pair orbital n y to the 3b 1 (*) orbital leads to the first excited singlet valence state 1 1 A 2 that has its 0-0 transition at 30 439.9145 cm Ϫ1 . 16 This dipole-forbidden transition has been the subject of many experimental studies [17][18][19][20] concentrating on aspects such as the role of vibronic coupling and interaction with triplet states. 16,21,22 The first Rydberg state derives from excitation of a lone pair electron to the 3s Rydberg orbital, giving rise to the 1 1 B 2 state located at 6.35 eV.…”

Use of the spatial phase of a focused laser beam to yield mechanistic information about photo-induced chemical reactions

“…The experimental onset of the π * ← n transition occurs at 3.75 eV, with a maximum at 4.38 eV. The threshold shifts down to 3.56 eV when singlet-triplet mixing is taken into account [11]. The vertical energies for transitions to the Rydberg states are 6.35 eV for n = 3 and 8.46 eV for n = 4 [12].…”