화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.114, No.3, 1398-1410, 2010
Stereodynamics at the Gas-Liquid Interface: Orientation and Alignment of CO2 Scattered from Perfluorinated Liquid Surfaces
Rotational orientation/alignment dynamics of CO2 scattered from a perfluorinated polyether (PFPE) liquid surface has been investigated via direct absorption experimental Studies and theoretical molecular dynamics (MD) simulations. Experimentally, polarization modulation of a single mode diode laser is combined with lock-in detection to measure circular/linear IR polarizance due to CO2 scattering from the surface at theta(inc) = 60 degrees and E-inc = 10.6(8) kcal/mol and probed over a series of final scattering angles, The differential absorption intensities are related through Fano-Macek theory to the three lowest multipole moments (A(0), A(2+), and O1-) which describe collisionally induced Orientation and alignment at the liquid surface. The total scattering population reflects both trapping-desorption (TD) and impulsive scattering (IS) components, with a strong positive anisotropy in the M-J distribution that indicates preferential CO2 scattering from the surface with a forward (i.e., "topspin") sense of end-over-end tumbling. Theoretical trajectory simulations provide 3D CO2 flux and J state distributions scattering from fluorinated self-assembled monolayers (F-SAMs) and are compared with experimental results as it function of final rotational state. Specifically, trends in the theoretical orientation/ alignment moments are in remarkable agreement over the full range of J states but with values consistently overpredicted by nearly 2-fold, which may reflect a higher level of local ordering for F-SAMS vs a gas-PFPE liquid interface.