Panel (a): Calculated fractional population of the five lowest rotational levels of D2O as function of rotational temperature. Close to Trot = 0 K, only the lowest rotational state of each of the two nuclear spin isomers (ortho and para) is populated in a 2:1 ortho:para ratio. Panel (b): Pyroelectric detector signal as function of excitation laser power monitoring the initial population of specific JKaKc-levels in a 1% D2O in He expansion for TN = 373 K. Each asymptote A of the power dependences (obtained from a fit of y = A(1-e−k(x-xc)) to the data) represents the population in the initial level of the indicated transition. Comparison of the two graphs yields a maximal excited fraction of 30% for the R11(1) transition.
D2O partial pressure changes in UHV chamber when a H2O or D2O ice surface is exposed to a D2O molecular beam (Et = 69 kJ/mol, θ = 60°, Ts = 108 K) in comparison to D2O scattering from an inert PTFE beam flag. Initially, when the D2O beam strikes with H2O surface, a larger pressure rise is detected (see insert) than for the three subsequent exposures when the ice surface is covered with D2O-ice. For the final exposure, the D2O beam is scattered off an inert flag (0% sticking) instead off the ice surface.
Ground state sticking probabilities of D2O on H2O- and D2O-ice as function of incident angle for Et = 38 kJ/mol and 69 kJ/mol. The D2O sticking probability decreases with increasing speed parallel to the surface. D2O trapping on H2O-ice is slightly (1%) lower than on D2O-ice. The error-bars indicate the standard deviation of at least three independent measurements.
D2O partial pressure rise during scattering of a D2O molecular beam (Et = 38 kJ/mol, normal incidence) from the D2O ice-covered surface (Ts = 108 K). Less than 1% of the incident D2O molecules are reflected. IR pumping of the antisymmetric OD-stretch normal mode of 25% of the incident molecules produces no detectable change in D2O partial pressure (red line indicates laser on/off).
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