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In molecular collisions, resonances occur at specific energies at which the colliding particles temporarily form quasibound complexes, resulting in rapid variations in the energy dependence of scattering cross sections. Experimentally, it has proven challenging to observe such scattering resonances, especially in differential cross sections. We report the observation of resonance fingerprints in the state-to-state differential cross sections for inelastic NO-He collisions in the 13 to 19 centimeter(-1) energy range with 0.3 centimeter(-1) resolution. The observed structures were in excellent agreement with quantum scattering calculations. They were analyzed by separating the resonance contributions to the differential cross sections from the background through a partitioning of the multichannel scattering matrix. This revealed the partial-wave composition of the resonances and their evolution during the collision.

We derive a quasiclassical expression for the density of states (DOS) of an arbitrary, ultracold, N -atom collision complex, for a general potential energy surface (PES). We establish the accuracy of our quasiclassical method by comparing to exact quantum results for the K 2 -Rb and NaK-NaK systems, with isotropic model PESs. Next, we calculate the DOS for an accurate NaK-NaK PES to be 0.124 µK −1 , with an associated Rice-Ramsperger-Kassel-Marcus (RRKM) sticking time of 6.0 µs. We extrapolate the DOS and sticking times to all other polar bialkali-bialkali collision complexes by scaling with atomic masses, equilibrium bond lengths, dissociation energies, and dispersion coefficients. The sticking times calculated here are two to three orders of magnitude shorter than those reported by Mayle et al. [Phys. Rev. A 85, 062712 (2012)]. We estimate dispersion coefficients and collision rates between molecules and complexes. We find that the sticking-amplified three-body loss mechanism is not likely the cause of the losses observed in the experiments. * gerritg@theochem.ru.nl arXiv:1905.06691v2 [cond-mat.quant-gas]

We present the first pair plus three-body potential of water from ab initio calculations that quantitatively reproduces the experimental far-infrared spectra of the water dimer and trimer. The dimer spectrum was obtained from the pair potential through rigorous six-dimensional quantum calculations of the vibration-rotation-tunneling levels. The three-body interactions, together with the pair potential, produce an accurate representation of the hydrogen bond torsional levels of the water trimer.

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