Two-photon excitation spectra of the higher lying m1 Ag states of octatetraene

The 2-photon excitation spectra of all-trans-octatetraene in n-hexane and n-octane host crystals at 1.8K have been recorded for the region 28 000 to 50 000 cm−1. On the basis of their frequencies, intensities, and solvent shift behaviors all of the bands in the region 28 000 to 40 000 cm−1 are assigned to vibronic bands of the 11 Ag – 21 Ag transition. Four bands are detected above 44 000 cm−1. Two of them must be assigned to 0-0 transitions from the 11 Ag ground state to the higher lying 1Ag states at 45 030 and 46 710 cm−1, respectively. The other two bands at 48 000 and 49 860 cm−1 could be either vibronic addition to the 0-0 band at 46 710 cm−1 or 0-0 bands for the new m1 Ag states.