ELECTRIC DICHROISM SPECTROSCOPY IN THE VACUUM ULTRAVIOLET .2. FORMALDEHYDE, ACETALDEHYDE, AND ACETONE

Electric field studies, including electric linear dichroism and electrochromism spectroscopy, have been completed for the second excited singlet of formaldehyde, acetaldehyde, and acetone in the gas phase. Transition-moment directions, excited-state dipole moments, and excited-state mean polarizabilities are determined. The data support the 3s ← n assignment for these bands. The excited-state dipole moment and mean polarizability determined for acetone are 0.19 D, electron density away from the oxygen, and 450 Å3, respectively. These values for formaldehyde are 0.33 D and 70 Å3, respectively. Excited-state parameters of this magnitude give additional support for the extravalent assignment. Acetaldehyde excited state properties cannot be determined quantitatively, but analysis of the spectrum gives some evidence that the transition moment of the absorption in question is in the molecular plane as would be expected for the 3s ← n Rydberg transition. Finally, strong perturbation of the transition-moment lengths suggests the presence of an underlying transition of the same symmetry as the second excited singlet. © 1979, American Chemical Society. All rights reserved.