Zillich, R.E.R.E.ZillichKwon, Y.Y.KwonWhaley, K.B.K.B.Whaley2022-03-032022-03-032004https://publica.fraunhofer.de/handle/publica/20737610.1103/PhysRevLett.93.2504012-s2.0-42749107959Rotational absorption spectra of acetylene in superfluid He-4 calculated using a path-integral correlation function approach are seen to result in an anomalously large distortion constant in addition to a reduced rotational constant, with values in excellent agreement with recent experiments. Semianalytic treatment of the dynamics with a combined correlated basis function-diffusion Monte Carlo method reveals that this anomalous behavior is due to strong coupling of the higher rotational states of the molecule with the roton and maxon excitations of He-4, and the associated divergence of the He-4 density of states in this region.en519003006530journal article