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Phonon sidebands of localized excitons in molecular crystals with methyl torsions: Hexamethylbenzene
dc.contributor.authorWoodruff, Steven D.en_US
dc.contributor.authorPrasad, Paras N.en_US
dc.contributor.authorKopelman, Raoulen_US
dc.date.accessioned2010-05-06T21:44:47Z
dc.date.available2010-05-06T21:44:47Z
dc.date.issued1974-03-15en_US
dc.identifier.citationWoodruff, Steven D.; Prasad, Paras N.; Kopelman, Raoul (1974). "Phonon sidebands of localized excitons in molecular crystals with methyl torsions: Hexamethylbenzene." The Journal of Chemical Physics 60(6): 2365-2369. <http://hdl.handle.net/2027.42/70173>en_US
dc.identifier.urihttps://hdl.handle.net/2027.42/70173
dc.description.abstractFluorescence and phosphorescence phonon sidebands of isotopic mixed hexamethylbenzene crystals at 2°K are presented. The external phonons can be observed separately from the semi‐internal (methyl torsion) ones. The nature of the electronic or vibronic state has observable but not drastic effects on the exciton‐phonon coupling function. Likewise, the exciton delocalization is of minor importance to the exciton‐phonon function in hexamethylbenzene. The coupling between external and internal vibrations is also weak in this system. The exciton‐phonon coupling appears comparable for the optical and acoustic phonons in hexamethylbenzene. The phonon sidebands give some of the phonon singularities of the low‐temperature crystal.en_US
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dc.format.extent379016 bytes
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dc.format.mimetypeapplication/pdf
dc.publisherThe American Institute of Physicsen_US
dc.rights© The American Institute of Physicsen_US
dc.titlePhonon sidebands of localized excitons in molecular crystals with methyl torsions: Hexamethylbenzeneen_US
dc.typeArticleen_US
dc.subject.hlbsecondlevelPhysicsen_US
dc.subject.hlbtoplevelScienceen_US
dc.description.peerreviewedPeer Revieweden_US
dc.contributor.affiliationumDepartment of Chemistry, The University of Michigan, Ann Arbor, Michigan 48104en_US
dc.description.bitstreamurlhttp://deepblue.lib.umich.edu/bitstream/2027.42/70173/2/JCPSA6-60-6-2365-1.pdf
dc.identifier.doi10.1063/1.1681371en_US
dc.identifier.sourceThe Journal of Chemical Physicsen_US
dc.identifier.citedreferenceJ. J. Rush and T. I. Taylor, J. Chem. Phys. 44, 2749 (1966).en_US
dc.identifier.citedreferenceJ. J. Rush, J. Chem. Phys. 47, 3936 (1967).en_US
dc.identifier.citedreferenceP. A. Reynolds, J. K. Kjems, and J. W. White, J. Chem. Phys. 56, 2928 (1972).en_US
dc.identifier.citedreferenceR. Kopelman, F. W. Ochs, and P. N. Prasad, J. Chem. Phys. 57, 5409 (1972).en_US
dc.identifier.citedreferenceH. Boutin and S. Yip, Molecular Spectroscopy with Neutrons (M.I.T. press, Cambridge, MA, 1968).en_US
dc.identifier.citedreferenceP. N. Prasad and R. Kopelman, J. Chem. Phys. 58, 126 (1973).en_US
dc.identifier.citedreferenceP. N. Prasad, S. D. Woodruff, and R. Kopelman, Chem. Phys. 1, 173 (1973).en_US
dc.identifier.citedreferenceP. N. Prasad and R. Kopelman, Chem. Phys. Lett. 21, 505 (1973).en_US
dc.identifier.citedreferenceP. N. Prasad and R. Kopelman, J. Chem. Phys. 58, 5704 (1973).en_US
dc.identifier.citedreferenceDr. J. E. Edmonds (private communication) has informed us that the neutron diffraction studies of the low temperature phase suggest a trigonal crystal form with one molecule per primitive cell and the unit cell containing symmetry elements CiCi and C3C3 (nearly hexagonal symmetry). Very recently Bertinelli and Stremmenos [J. Chem. Soc. Faraday II, 69, 889 (1973)] agreed with this structure. Even though our7 interpretation of the Raman spectra disagrees sharply with theirs, our interpretation is also consistent with S6S6 symmetry (with the effective phonon force field being close to a D3dD3d or even D6hD6h symmetry).en_US
dc.identifier.citedreferenceThis is derived from the fact that the RzRz libration involves the lowest moment of inertia. Also, as this motion has a nearly sixfold barrier, its force constant is expected to be the softest of all the librations. Furthermore, for the high temperature triclinic form where a nearly hexagonal arrangement is seen in the plane 001 (the low temperature and high temperature crystal forms probably only differ in the packing of these planes), the calculation based on root mean square amplitude as derived from the neutron diffraction studies [W. C. Hamilton, J. E. Edmonds, A. Trippe, and J. J. Rush, Discuss. Faraday Soc. 48, 192 (1969)] shows that the RzRz libration should be the lowest frequency libration. However, it is possible that this simple picture is not valid, and the RzRz libration is not below the RxRx and RyRy librations but rather lies in the region above 100 cm−1100cm−1 for the HMB‐d18HMB‐d18 crystal. Even so, this would not affect our basic conclusions given below.en_US
dc.identifier.citedreferenceR. M. Hochstrasser and P. N. Prasad, J. Chem. Phys. 56, 2814 (1972).en_US
dc.identifier.citedreferenceWe have done a concentration dependence study on the fluorescence going below 0.6% and above 10% of HMB‐h18.HMB‐h18.en_US
dc.identifier.citedreferenceFinally, it is also possible that the RzRz libration lies in this region (see Ref. 11). In such a situation some of the features above 120 cm−1120cm−1 would be derived from the one phonon transitions of the RzRz librational branch. The doublet feature around 200 cm−1200cm−1 is due to internal vibrations.en_US
dc.identifier.citedreferenceEven if the individual coupling function CS,qfCS,qf has an oscillatory behavior when plotted against q, Eq. (1) contains a summation of such functions at each energy point (with a given ω whose width is defined by the experimental resolution). We believe that the summation over such functions will average out such oscillations, resulting in an effective smoothing of these features, except when directly related to singularities.en_US
dc.identifier.citedreferenceA comparison of the above frequencies with those of the neat crystal sidebands will be given in a future publication.en_US
dc.owningcollnamePhysics, Department of


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