Experimental and theoretical studies of the Xe-OH(A/X) quenching system

New multi-reference, global ab initio potential energy surfaces (PESs) are reported for the interaction of Xe atoms with OH radicals in their ground X²Π and excited A²Σ⁺ states, together with the non-adiabatic couplings between them. The 2A' excited potential features a very deep well at the collinear Xe-OH configuration whose minimum corresponds to the avoided crossing with the 1A' PES. It is therefore expected that, as with collisions of Kr + OH(A), electronic quenching will play a major role in the dynamics, competing favorably with rotational energy transfer within the 2A' state. The surfaces and couplings are used in full three-state surface-hopping trajectory calculations, including roto-electronic couplings, to calculate integral cross sections for electronic quenching and collisional removal. Experimental cross sections, measured using Zeeman quantum beat spectroscopy, are also presented here for comparison with these calculations. Unlike similar previous work on the collisions of OH(A) with Kr, the surface-hopping calculations are only able to account qualitatively for the experimentally observed electronic quenching cross sections, with those calculated being around a factor of two smaller than the experimental ones. However, the predicted total depopulation of the initial rovibrational state of OH(A) (quenching plus rotational energy transfer) agrees well with the experimental results. Possible reasons for the discrepancies are discussed in detail.

An experimental study of OH(A2Σ+) + H2: Electronic quenching, rotational energy transfer, and collisional depolarization

Zeeman quantum beat spectroscopy has been used to determine the thermal (300 K) rate constants for electronic quenching, rotational energy transfer, and collisional depolarization of OH(A²Σ⁺) by H₂. Cross sections for both the collisional disorientation and collisional disalignment of the angular momentum in the OH(A²Σ⁺) radical are reported. The experimental results for OH(A²Σ⁺) + H₂ are compared to previous work on the OH(A²Σ⁺) + He and Ar systems. Further comparisons are also made to the OH(A²Σ⁺) + Kr system, which has been shown to display significant non-adiabatic dynamics. The OH(A²Σ⁺) + H₂ experimental data reveal that collisions that survive the electronic quenching process are highly depolarizing, reflecting the deep potential energy wells that exist on the excited electronic state surface.

Lack of association between gastric emptying of solids and symptoms in nonulcer dyspepsia

Gastric motor dysfunction and concomitant gastric stasis have been implicated in the pathogenesis of nonulcer dyspepsia, but a cause-and-effect relationship is not established. Essential dyspepsia refers to a subgroup of nonulcer dyspepsia patients who have no evidence of irritable bowel syndrome, gastroesophageal reflux, or pancreaticobiliary disease. In 32 patients with essential dyspepsia, and 32 randomly selected dyspepsia-free community controls of similar age and sex, we measured gastric emptying of solids using Tc99m-Sulphur Colloid in a fried egg sandwich. Subjects with neuromuscular or other diseases that may alter gastric emptying were excluded. Symptoms were assessed by a standard questionnaire. Data processing was carried out "blinded" to the subjects' clinical status. Female patients took significantly longer to empty half the initial stomach activity (mean 90 min) than female controls (mean, 73 min; p = 0.02). The rate of emptying at 25 min was also significantly less in female patients than in controls. Female and male controls, and male patients, had similar emptying times. Delayed emptying was not associated with the occurrence of postprandial pain, belching, or nausea; there was a trend for the half-time rate of emptying to be greater in patients with abdominal distention. While gastric emptying of solids is slightly delayed in females with essential dyspepsia as a group, this may not explain their symptoms.