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Rotationally Resolved Studies of the Exciton Coupled S1/S2 Origin Regions of Diphenylmethane and the d12 Isotopologue



David F. Plusquellic, Kevin O. Douglass, Jaime Stearns, Nathan Pillsbury, Timothy Zwier, Christian Muller


Rotationally resolved microwave and ultraviolet spectra of jet-cooled diphenylmethane (DPM) and DPM-d^12 have been obtained in S0, Sd1 and S2 electronic states using Fourier-transform microwave and UV laser/molecular beam spectrometers. The S0 and S1 states of both isotopologues have been well-fit to asymmetric rotor Hamiltonians that include only Watson distortion parameters. The transition dipole moment (TDM) orientations of DPM and DPM-d12 are perpendicular to the C2 symmetry axes with 66(2) : 34(2) % ac-type character establishing the lower exciton S1 origin as completely delocalized and the anti-symmetric combination of the zero-order locally excited states. In contrast, similar b-type rotational fits of the upper excitonic S2 origin bands at S1 + 123 cm-1 and S1 + 116 cm 1, respectively, were not possible in line with expectations from previous work [N. R. Pillsbury, J. A. Stearns, C. W. Müller, T. S. Zwier and D. F. Plusquellic, J. Chem Phys., in press.] where the S2 origins were found to be largely perturbed though vibronic interactions with the S1 symmetric (T), anti-symmetric torsional ( ) and butterfly (β) levels in close proximity. The symmetry and character of the mixed S1 |v(T), v( ), v(β)> levels previously assigned in DPM include |0,5,0>, |2,3,0>, |4,1,0> and |0,3,1> suggesting Fermi and/or Coriolis interactions as possible coupling mechanisms for such strong mixing between vibronic levels with Δν(T) and/or Δν( ) > 1. The observed TDM components and exciton splitting from these studies are shown to be in poor agreement with predictions from the dipole coupling model and TDDFT ab initio methods.
Journal of Chemical Physics


Exciton Interactions, Exciton Coupling, Dipole Coupling Model, Rotationally Resolved UV Spectroscopy.


Plusquellic, D. , Douglass, K. , Stearns, J. , Pillsbury, N. , Zwier, T. and , C. (2008), Rotationally Resolved Studies of the Exciton Coupled S1/S2 Origin Regions of Diphenylmethane and the d12 Isotopologue, Journal of Chemical Physics, [online], (Accessed May 30, 2024)


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Created December 9, 2008, Updated January 27, 2020