Optically detected magnetic resonance spectra of the lowest triplet states of benzophenone, /sup 13/C-benzophenone, and three 4,4'-dihalobenzophenones

Journal Article · Wed Jun 15 04:00:00 EDT 1977 · J. Chem. Phys.; (United States)

OSTI ID:7291941

Mucha, J A; Pratt, D W

We describe measurements of the complete angular dependence of the optically detected magnetic resonance (ODMR) spectra of the lowest triplet states of benzophenone, carbonyl-/sup 13/C-benzophenone, 4,4'-difluorobenzophenone, 4,4'-dichlorobenzophenone, and 4,4'-dibromobenzophenone in 4,4'-dibromodiphenylether host crystals at liquid helium temperatures. The principal axes and values of D (including the absolute signs) and g are reported and used to evaluate the spin--spin and spin--orbit contributions to the fine-structure tensor of the parent molecule. It is found that the dipolar contributions to D in /sup 3/(n,..pi..*) benzophenone are at least a factor of 2 less than recent ab initio estimates of the spin--spin contributions to D in /sup 3/A/sub 2/ formaldehyde. Carbon-13 hyperdfine splittings have been observed in the ODMR spectra of /sup 13/C-benzophenone; an analysis of these yields estimates of the orbital spin densities rho/sub 2//sub s//sup() CO/approx. =0.008 and rho/sub 2//sub p/x-italic/sup() CO/< or =0.14 and suggests that the C/sub 1/--C(O) --C/sub 1/' fragment is planar. The fine-structure parameters of triplet benzophenone are strongly influenced by halogen atoms in the para ring positions. The ODMR spectra of the 4,4'-difluoro and 4,4'-dibromo derivatives also exhibit ring halogen atom hyperfine structure from which the estimate rho/sub 2//sub p/..pi../sup C/4> or =0.10 is obtained. Taken together, the results of this investigation suggest that as much as 50% of the total spin density in the lowest triplet state of benzophenone itself resides on the aromatic rings, thereby accounting for the reduction in the dipolar contributions to D in the parent molecule and for the changes in the principal values (and directions) of D which occur in its heavy-atom substituted derivatives.

• Research Organization: Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
• OSTI ID: 7291941
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 66:12; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500 -- Photochemistry
640300* -- Atomic
Molecular &amp; Chemical Physics
74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION SPECTRA
BENZOPHENONE
ENERGY LEVELS
EXCITED STATES
KETONES
LUMINESCENCE
MAGNETIC RESONANCE
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
PHOSPHORESCENCE
RESONANCE
SPECTRA