title: Resonance-Enhanced Raman Scattering of Ring-Involved Vibrational Modes in the (1)B(2u) Absorption Band of Benzene, Including the Kekule Vibrational Modes ν(9) and ν(10).
abstract: Resonance Raman spectroscopy provides much stronger Raman signal levels than its off-resonant counterpart and adds selectivity by excitation tuning. Raman preresonance of benzene has been well studied. On-resonance studies, especially at phonon-allowed absorptions, have received less attention. In this case, we observe resonance of many of the vibration modes associated motion of the carbons in the ring while tuning over the (1)B2u absorption, including the related ν9 (CC stretch Herzberg notation, ν14 Wilson notation) and ν10 (CH-parallel bend Herzberg notation, ν15 Wilson notation) vibrational modes along with the ν2 (CC-stretch or ring-breathing Herzberg notation, ν1 Wilson notation) mode and multiples of the ν18 (CCC-parallel bend Herzberg notation, ν6 Wilson notation) vibrational mode. The ring-breathing mode is found to mix with the b2u modes creating higher frequency composites. Through the use of an optical parametric oscillator (OPO) to tune through the (1)B2u absorption band of liquid benzene, a stiffening (increase in energy) of the vibrational modes is observed as the excitation wavelength nears the (1)B2u absorption peak of the isolated molecule (vapor) phase. The strongest resonance amplitude observed is in the 2 × ν18 (e2g) mode, with nearly twice the intensity of the ring-breathing mode, ν2. Several overtones and combination modes, especially with ν2 (a1g), are also observed to resonate. Raman resonances on phonon-allowed excitations are narrow and permit the measurement of vibrations not Raman-active in the ground state.
authors.affiliation: The Pennsylvania State University , School of Electrical Engineering and Computer Science, State College, Pennsylvania 16802, United States.
authors.forename: Adam H
authors.initials: AH
authors.lastname: Willitsford
authors.affiliation: The North Carolina State University , Department of Physics, Raleigh, North Carolina 27695-8202, United States.
authors.forename: C Todd
authors.initials: CT
authors.lastname: Chadwick
authors.affiliation: The Pennsylvania State University , School of Electrical Engineering and Computer Science, State College, Pennsylvania 16802, United States.
authors.forename: Stewart
authors.initials: S
authors.lastname: Kurtz
authors.affiliation: The Pennsylvania State University , School of Electrical Engineering and Computer Science, State College, Pennsylvania 16802, United States.|The North Carolina State University , Department of Physics, Raleigh, North Carolina 27695-8202, United States.
authors.forename: C Russell
authors.initials: CR
authors.lastname: Philbrick
authors.affiliation: The North Carolina State University , Department of Physics, Raleigh, North Carolina 27695-8202, United States.
authors.forename: Hans
authors.initials: H
authors.lastname: Hallen