Molecular beam scattering of ammonia from a dodecane flat liquid jet.

The evaporation and scattering of ND3 from a dodecane flat liquid jet are investigated and the results are compared with previous studies on molecular beam scattering from liquid surfaces. Evaporation is well-described by a Maxwell-Boltzmann flux distribution with a cos θ angular distribution at the liquid temperature. Scattering experiments at Ei = 28.8 kJ mol-1 over a range of deflection angles show evidence for impulsive scattering and thermal desorption. At a deflection angle of 90°, the thermal desorption fraction is 0.49, which is higher than that of other molecules previously scattered from dodecane and consistent with work performed on NH3 scattering from a squalane-wetted wheel. ND3 scattering from dodecane results in super-specular scattering, as seen in previous experiments on dodecane. The impulsive scattering channel is fitted to a "soft-sphere" model, yielding an effective surface mass of 55 amu and an internal excitation of 5.08 kJ mol-1. Overall, impulsively scattered ND3 behaves similarly to other small molecules scattered from dodecane.

Evaporation and scattering of neon, methane, and water from a dodecane flat liquid jet.

The evaporation and scattering of Ne, CD4, and D2O from a dodecane flat liquid jet are investigated in a molecular beam apparatus. The experiment yields translational energy distributions as a function of scattering angle by means of a rotatable mass spectrometer. In the evaporation experiments, one observes a Maxwell-Boltzmann distribution with a cos θ angular distribution superimposed on a weak, isotropic background. The scattering experiments show contributions from impulsive scattering and thermal desorption. At select incident angles for the three systems, angular distributions show super-specular scattering for the impulsive scattering channel, an effect attributed to anisotropic momentum transfer to the liquid surface. The impulsive scattering channel is analyzed with a soft-sphere model to explore energy transfer between the scatterer and liquid as a function of deflection angle. Compared to Ne scattering, the polyatomic gases exhibit more thermal desorption and, in the impulsive scattering channel, a higher degree of internal excitation.

Photodissociation of iso-propoxy (i-C3H7O) radical at 248 nm.

Photodissociation of the i-C3H7O radical is investigated using fast beam photofragment translational spectroscopy. Neutral i-C3H7O radicals are produced through the photodetachment of a fast beam of i-C3H7O- anions and are subsequently dissociated at 248 nm (5.0 eV). The dominant product channels are CH3 + CH3CHO and OH + C3H6 with some contribution from H + C3H6O. The CH3 and H loss channels are attributed to dissociation on the ground electronic state of i-C3H7O, but in a nonstatistical manner because calculated RRKM dissociation rates exceed the rate of energy randomization. Translational energy and angular distributions for OH loss are consistent with ground state dissociation, but the branching ratio for this channel is considerably higher than predicted from RRKM rate calculations. Additionally, i-C3H7O undergoes three-body fragmentation to CH3 + CH3 + HCO and CH3 + CH4 + CO. These three-body channels are attributed to dissociation of i-C3H7O to CH3 + CH3CHO, followed by secondary dissociation of CH3CHO on its ground electronic state.