Figure 2.
a) The three low‐barrier tunneling motions of the water dimer. The acceptor switching (AS) involving an exchange of the two protons of the proton acceptor, the interchange (IC) exchanging the proton donor and proton acceptor, and the bifurcation (BI) tunneling. b) Owing to AS, each energy level is split into two energy levels. The symmetries are denoted in the irreducible representations of the G 4 MS group. IC tunneling leads to an additional splitting into three energy levels labeled within the irreducible representations of the G 16 MS group. BI causes a shift of the energy levels. c) VRT levels for K a=0 and K a=1 in the vibrational ground. At 0.37 K, only VRT levels represented as solid lines are expected to be significantly populated. In parentheses, the spin statistical weights are shown.