Methane dissociative chemisorption and detailed balance on Pt(111): dynamical constraints and the modest influence of tunneling.

A dynamically biased (d-) precursor mediated microcanonical trapping (PMMT) model of the activated dissociative chemisorption of methane on Pt(111) is applied to a wide range of dissociative sticking experiments, and, by detailed balance, to the methane product state distributions from the thermal associative desorption of adsorbed hydrogen with coadsorbed methyl radicals. Tunneling pathways were incorporated into the d-PMMT model to better replicate the translational energy distribution of the desorbing methane product from the laser induced thermal reaction of coadsorbed hydrogen and methyl radicals occurring near T(s) = 395 K. Although tunneling is predicted to be inconsequential to the thermal dissociative chemisorption of CH4 on Pt(111) at the high temperatures of catalytic interest, once the temperature drops to 395 K the tunneling fraction of the reactive thermal flux reaches 15%, and as temperatures drop below 275 K the tunneling fraction exceeds 50%.

Communication: angle-resolved thermal dissociative sticking of CH4 on Pt(111): further indication that rotation is a spectator to the gas-surface reaction dynamics.

Effusive molecular beam measurements of angle-resolved thermal dissociative sticking coefficients for CH(4) impinging on a Pt(111) surface, at a temperature of 700 K, are reported and compared to theoretical predictions. The reactivity falls off steeply as the molecular angle of incidence increases away from the surface normal. Successful modeling of the thermal dissociative sticking behavior, consistent with existent CH(4) supersonic molecular beam experiments involving rotationally cold molecules, required that rotation be treated as a spectator degree of freedom.

An effusive molecular beam technique for studies of polyatomic gas-surface reactivity and energy transfer.

An effusive molecular beam technique is described to measure alkane dissociative sticking coefficients, S(T(g), T(s); ϑ), on metal surfaces for which the impinging gas temperature, T(g), and surface temperature, T(s), can be independently varied, along with the angle of incidence, ϑ, of the impinging gas. Effusive beam experiments with T(g) = T(s) = T allow for determination of angle-resolved dissociative sticking coefficients, S(T; ϑ), which when averaged over the cos (ϑ)/π angular distribution appropriate to the impinging flux from a thermal ambient gas yield the thermal dissociative sticking coefficient, S(T). Nonequilibrium S(T(g), T(s); ϑ) measurements for which T(g) ≠ T(s) provide additional opportunities to characterize the transition state and gas-surface energy transfer at reactive energies.

Carcinoid tumor presenting as a primary mesenteric mass: a case report and review of the literature.

We report a case of a primary carcinoid tumor arising in the mesentery of the small bowel of a 52-year-old man. The mesenteric mass in this patient was first identified as an incidental finding on CT imaging for bilateral nephrolithiasis. As a result of the abnormal findings, follow-up evaluation identified a partially calcified lobulated mesenteric lymph node.

An unusual abdominal tumor--leiomyosarcoma of the mesentery: a case report.

We report the case of an 82-year-old woman who presented with an ill-defined mass and tenderness in the right lower quadrant of the abdomen. On computerized tomography scan, she had an irregular large bosselated mass of the mesentery located medial to the cecum and associated with multiple loops of small intestine. Preoperative differential diagnoses included leiomyosarcoma, lymphoma and gastrointestinal stromal tumor.