High-resolution one and two photon excitation spectra of t r a n s, t r a n s-1,3,5,7-octatetraene

Abstract

One and two photon excitation spectra for the lowest energy singlet transition (2 ¹A_g←1 ¹A_g) of trans, trans 1,3,5,7‐octatetraene in n‐octane at 4.2 K(0–0 at 28 56l cm⁻¹) have been measured and analyzed. The one photon spectrum is found to be vibronically induced while the two photon spectrum is electronically allowed. The contribution of the higher lying 1 ¹B_u←1¹A_g transition (0–0 at approximately 32 100 cm⁻¹) to the observed two photon excitation spectrum is found to be negligible allowing vibrational overtones of the 2 ¹A_g←1 ¹A_g system to be observed. On the bases of frequency, intensity, and one or two photon allowedness, 128 measured lines are assigned as combinations of 4 antisymmetric and 11 symmetric normal modes.