Laser induced fluorescence spectra of the D 1∑u+→B′ 1∑g+ and C 1Πg→A 1∏u systems of C2 in solid Ne

Abstract

In our study of carbon vapor molecules trapped in Ne matrices at 6 K, we observed laser induced fluorescence spectra of the D 1∑u+→B′ 1∑g+ system of C2 upon excitation of the Mulliken transition D 1∑u+←X 1∑g+ of C2 at 232 nm. A vibrational progression was clearly observed going from the upper vibrational v′=0 level of the electronic D state into several lower v″=0–6 levels of the B′ state. We found that the progression spans from 359 to 517 nm with a large Franck–Condon shift showing the intensity maximum for the 0–2 or 0–3 transition. The vibrational constants for the B′ state were derived as ωe=1427 cm−1 and ωexe=2.1 cm−1. We also observed the C→A and the Swan band emissions, showing that from the excited D state also additional states were populated by internal conversion and intersystem crossing. The constants for the A state were derived as ωe=1613.5 cm−1 and ωexe=18.5 cm−1. Fluorescence excitation spectra of the D→B′ vibronic transitions were found to reproduce well the relatively narrow absorption feature of the Mulliken D←X system. We discuss the entirely different excitation spectra occurring in argon matrices in terms of matrix-site effects. Each vibronic band of the D→B′ progression shows fine structures probably due to translations and librations of C2 molecules coupled with the surrounding lattice of Ne atoms.