Fluorescence excitation and hole-burning spectra of jet-cooled tropolone-M (M = N2, CO) van der Waals complexes: Structures and proton tunneling in the S1 state

Proton tunneling in the S1 state of jet-cooled tropolone−(N2)n (n = 1, 2) and tropolone−(CO)1 van der Waals complexes is investigated by measuring the hole-burning and fluorescence excitation spectra in the S1−S0 region. The hole-burning spectra enabled us to separate three overlapping absorption systems due to transitions between low-wavenumber and high-wavenumber tunneling doublet components of tropolone−(N2)1 and those of tropolone−(N2)2. The 0−0 tunneling doublet splitting of tropolone−(N2)1 has been confirmed to be 9.7 cm-1. It has been suggested that the magnitude of the tunneling splitting depends on the excited intermolecular vibrational level. In addition to the sandwich isomer I for tropolone−(N2)2 observed previously, a second isomer [II] has been identified. A much smaller microscopic red shift (−57.9 cm-1) than the corresponding value (−129.0 cm-1) for isomer I indicates that two N2 molecules are on the same side of the tropolone ring in isomer II. No tunneling splitting has been observed for...