Proton tunneling in the tropolone-N2 van der Waals complex

Proton tunneling splitting has been measured for the S0 → S1 origin band of the tropolone: N2 van der Waals complex by recording its laser-induced fluorescence excitation spectrum in a supersonic jet. A large decrease in the magnitude of the tunneling splitting, from 19.4 cm−1 in bare tropolone to 6.0 cm−1 in the 1:1 complex, has been observed, indicating that nitrogen perturbs the reaction coordinate by significantly increasing the barrier height in the excited state. Strong coupling of the tunneling mode to the in-plane N2 torsional mode is the likely source of this effect.