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It is routine practice to perform colonoscopy as a follow-up after an attack of diverticulitis, with the main aim to exclude any underlying malignancy.

The pulsed field ionization-photoelectron PFI-PE spectrum of boron trichloride BCl3 in the region of 93 590–95 640 cm−1has been measured using vacuum ultraviolet VUV laser. At energies 0–1100 cm−1above the adiabatic ionization energy IE of BCl3, the bending vibration progression of BCl3is clearly resolved in the PFI-PE spectrum, whereas the spectrum at energies 1200–1900 cm−1above the IEBCl3 is found to exhibit dense vibrational structure. This observation unambiguously shows that BCl3in its ground state has C2Vsymmetry. Ab initiocalculations performed at the CCSDTCBS level with high-level corrections are consistent with this observation, indicating that the BCl3X 2B2 ground state has two long and one short B–Cl bonds. Furthermore, the CCSDTCBS calculations predict the existence of two BCl3transitional structures with D3hand C2Vsymmetries lying 800 and 1300 cm−1, respectively, above the BCl3X 2B2 ground state. This prediction is also consistent with the dense features observed in the PFI-PE spectrum in the region of 1200–1900 cm−1above the IEBCl3. The assignment of the PFI-PE vibrational bands gives the IEBCl3 93 891 ± 2 cm−111.6410 ± 0.0003 eV and the bending frequencies for BCl3X 2B2, ν1b2 194 cm−1and ν1a1 209 cm−1. We have also examined the dissociative photoionization process BCl3hν→ BCl2 Cl e−using the synchrotron based PFI-PE-photoion coincidence method, yielding the 0 K threshold or appearance energy AE for this process to be 12.495 ± 0.002 eV. Combining this 0 K AE value and the IEBCl3, we have determined the 0 K bond dissociation energy D0 for Cl2B–Cl as 0.854 ± 0.002 eV. This experimental and theoretical study indicates that the CCSDT, FullCBS calculations with high-level corrections are highly reliable for the predictions of IEBCl3, AEBCl2 and D0Cl2B–Cl with error limits of less than 35 meV. However, the CCSDT, FullCBS predictions for ΔHf0°BCl3, ΔHf0°BCl2, and ΔHf0°BCl3 are less reliable with discrepancies up to 0.1 eV as compared to the experimental determinations.

Soluble and insoluble polystyrene-bound triphenylarsine reagents have been prepared from 4-styryldiphenylarsine. The utility of these reagents as ligands for palladium in Suzuki cross-coupling reactions is demonstrated. In these applications, the use of polymeric triphenylarsine simplifies the purification of the coupled product and allows for the ligand to be recycled. Furthermore, the soluble polymeric arsine reagent permits the palladium catalyst to be recovered and reused.

The collision-induced dissociation (CID) reaction of CH3SCH3⁺ + Ar was studied in a triple-quadrupole, double-octopole ion−molecule reaction apparatus. The absolute total cross sections for the product ions CH2SH⁺/CH3S⁺, CH2S⁺, CHS⁺, and CH3⁺ formed in the CID reaction have been measured in the center-of-mass kinetic energy (Ecm) range of 1−19 eV. Using the charge-transfer probing technique, we found that mass-47 product ions are formed in both the CH2SH⁺ and CH3S⁺ structures. The onsets for CH2SH⁺, CH3S⁺, CH2S⁺, CHS⁺, and CH3⁺ are consistent with their thermochemical thresholds. The formation of the higher-energy product channel CH3S⁺ + CH3, which involves C−S bond scission, is found to dominate in the Ecm range immediately above its onset. The lower-energy channel corresponding to the formation CH3SCH2⁺ + H is not found. The strong preference observed for the higher-energy channel is in accordance with the conclusions obtained from the CID studies of CH3SH⁺ and CH3CH2SH⁺, providing further evidence that the CID of CH3SCH3⁺ is also nonstatistical. The high yield of CH3S⁺ + CH3 is attributed to the more efficient translational-to-vibrational energy transfer for the C−S stretching modes with lower frequencies than to those for the C−H stretching modes with higher frequencies, along with weak coupling between these vibrational modes with significantly different frequencies of CH3SCH3⁺. In addition, the dissociation pathways deduced are consistent with the results of ab initio calculations at the G3 level.

The structures and energetics of the dichlorine oxides, Cl2On, n = 1−7, and their cations have been investigated theoretically at the Gaussian-2 (G2) and the Gaussian-3 (G3) levels of theory. The G2 and G3 heats of formation obtained for both neutral and cationic species allow the interpretation of assigned appearance energies and ionization energies reported in a recent photoionization mass spectrometric study (Rühl et al. Int. J. Mass Spectrom. 1999, 185, 545) on these chlorine oxides. The calculations predict that Cl2O6⁺ dissociates spontaneously to ClO2⁺ and ClO4, in agreement with the nonobservation of Cl2O6⁺ in the experimental study by Rühl et al. For systems with n ≤ 4, the calculated and experimental thermochemical properties (such as heats of formation and ionization energies) are in good to excellent agreement with each other. However, this agreement deteriorates as the size of the molecular system increases or as n exceeds 4. Thus it appears that the G3 method may also suffer from “an unfavorable accumulation of component small errors,” as has been found for the G2 method and its variants.

A detailed computational study on the structures, energetics, and reactions of the isomers of the [C2H3S] radical and the [C2H3S]⁺ cation has been carried out. The computational models used are slightly modified versions of the ab initio Gaussian-2 method. Ten [C2H3S] isomers have been identified. Among them, the thioformylmethyl radical (1) has the lowest energy, with a ΔHf0 value of 214 kJ mol^-1. Other more chemically important isomers include the thioacetyl radical (2), thiiranyl radical (4), 1-thiovinyl radical (8), and 2-thiovinyl radical (11, 12, 13, 14); the ΔHf0 values for these isomers are 251, 301, 314, and 342−347 kJ mol^-1, respectively. In addition, we have also studied various reactions involving these radicals. For instance, it is found that isomerization reactions of 1 to 2, 4, 8, and 12 have barriers ranging from 123 to 227 kJ mol^-1. On the other hand, reaction 2 → 3 proceeds via a dissociation/recombination mechanism:  2 → CS + CH3 → 3. The dissociation process is the rate-determining step, with a barrier of 187 kJ mol^-1. On the [C2H3S]⁺ potential energy surface, 12 isomers have been found. Among them, 2⁺ has the lowest energy, with a ΔHf0 value of 891 kJ mol^-1. Other isomers with ΔHf0 values within 200 kJ mol^-1 of that of 2⁺ include 8⁺, 4⁺, 5⁺, 1t⁺ (triplet state of 1⁺), and S-protonated ethynylthiol (16⁺). Reactions involving these cations studied in this work include:  4⁺ → 2⁺ (barrier being 116 kJ mol^-1) and 4⁺ → 8⁺ (152 kJ mol^-1), both having 1⁺ as the transition structure; 1,2-H shift reaction 4⁺ → 5⁺ (219 kJ mol^-1); 1,3-H shift reaction 8⁺ → 16⁺ (232 kJ mol^-1); 8⁺ → 2⁺/4⁺ (162 kJ mol^-1); and 8⁺ → 5⁺ (171−175 kJ mol^-1) with two distinct pathways. The ΔHf0 values for various species calculated in this work are in good accord with available experimental measurements. Furthermore, the kinetics data reported here for reactions involving [C2H3S]⁺ cations are consistent with the results obtained in low-energy collision activated dissociation experiments.

An ab initio study on the structures and energetics of the carbonyl chloride radical and its dimer, oxalyl chloride, along with their cations, was carried out using the Gaussian-2 (G2) and Gaussian-3 (G3) models of theory. The structural results obtained include optimized geometries of ClCO, ClCO⁺, the anti, syn, and gauche conformers of (ClCO)2 and the transition structure (TS) connecting the anti and gauche conformers, and (ClCO)2⁺. The energetic results reported include the heats of formation for ClCO, various (ClCO)2 conformers and transition structures, ClCO⁺, and (ClCO)2⁺, as well as the adiabatic and vertical ionization energies of ClCO and (ClCO)2. The G3 results obtained are in very good agreement with the available experimental data. In some cases, where the experimental data are unavailable or imprecise, the G3 results should be reliable estimates. Among the three experimental ΔH^of298 values for ClCO found in the literature, the one most recently reported (−21.8 ± 2.5 kJ mol^-1) has the best agreement with the G3 result (−19.4 kJ mol^-1). For oxalyl chloride, we located a gauche conformer and a TS linking the anti and gauche conformers at the MP2(Full)/6-311+G(3df,2p) level, in qualitative agreement with the experimental findings. Also, both experimental and computational results agree that both the anti and gauche conformers lie in very flat potential minima. Based on the limited number of systems studied in this work, the G3 model yields results which are in better agreement with the experimental data than the G2 method.

The [C2H5O^-] potential energy surface has been investigated with a modified Gaussian-2 methodology, the G2++ approximation. Eight stable [C2H5O^-] isomers have been found on the surface:  CH3CH2O^- (1^-), W−CH3CHOH^- (2^-), Y−CH3CHOH^- (3^-), Y−CH2OCH3^- (4^-), W−CH2OCH3^- (5^-), ZE-CH2CH2OH^- (6^-), EE-CH2CH2OH^- (7^-), and EZ-CH2CH2OH^- (8^-). Among these isomers, 1^- is the most stable thermodynamically. The calculated G2++ heats of formation for the isomeric anions are in very good accord with the available experimental data. Also studied with the same ab initio method are the various rearrangements among the eight isomers and the fragmentation pathways of 1^-. Among the reactions involving 1^-, the fragmentation process 1^- → H2 + CH2CHO^- has the least barrier. This result is in total agreement with the experimental collision activated dissociation and infrared multiple photon induced elimination studies of the ethoxide anion.

The photoionization and dissociative photoionizations of ethylene oxide have been studied both experimentally and theoretically. In experiments, photoionization efficiency spectra for ions C2H4O⁺, C2H3O⁺, C2H2O⁺, C2HO⁺, CH3O⁺, CH2O⁺, CHO⁺, C2H4⁺, C2H3⁺, C2H2⁺, C2H⁺, CH4⁺, CH3⁺, CH2⁺, CH⁺, and C⁺ have been obtained. In addition, the energetics of the dissociative photoionizations have been examined by ab initio Gaussian-2 calculations. The computational results are useful in establishing the dissociation channels near the ionization thresholds. The dissociation channels established may be broadly divided into two types:  simple bond cleavage reactions and those involving transition structures and activation energies.

The photoionization and dissociative photoionizations of propylene oxide have been studied both experimentally and theoretically. In experiments, photoionization efficiency spectra for ions C3H6O⁺, C2H3O⁺, CH3O⁺, CH2O⁺, CHO⁺, C2H4⁺, C2H3⁺, C2H2⁺, CH3⁺, and CH2⁺ were obtained. Theoretically, the energetics of the dissociative photoionizations were examined by ab initio Gaussian-2 calculations. The computational results are useful in our attempt to establish the dissociation channels near the ionization thresholds. The dissociation channels we propose include simple bond cleavage reactions as well as reactions involving intermediates and transition structures.

The structures and energetics of the C2H2N and C2H2N⁺ isomers have been investigated using a modified Gaussian-2 (G2) method, which takes into account the energy correction due to spin contamination. At the QCISD(Full)/6-31G(d) level, C2H2N may exist as 12 stable isomers. In the order of decreasing stabilities, they are CH2CN (1), CH2NC (2), CHCNH (3), c-CH2CN (4), c-NCHCH (5), CHNCH (6), NH2CC (7), NHCHC (9), c-NHCHC (10), cis-CHCHN (12), cis-CHNHC (13), and trans-CHNHC (14). On the other hand, there are seven C2H2N⁺ isomers. In the order of decreasing stabilities, they are c-NCHCH⁺ (5⁺), CH2CN⁺ (1⁺), CH2NC⁺ (2⁺), CHCNH⁺ (3⁺), CHNCH⁺ (6⁺), c-NHCHC⁺ (10⁺), and NH2CC⁺ (7⁺). The G2 result for the ionization energy of 1 and the ΔH°f298 values of 1 and 1⁺ are in good agreement with the available experimental data. However, the G2 results for radicals 2 and 5 as well as cations 2⁺ and 5⁺ do not agree with the experimental data in the literature. This calls for a reexamination of the experimental results. Furthermore, in a recent study of the reaction between nitrogen atom and vinyl radical, a C2H2N radical was formed with an ionization energy < 9.64 eV. On the basis of our calculations and known reactivity of the reactants, it is concluded that the unidentified isomer is likely to be 2.

We reviewed the intraventricular cardiac tumors presenting at our institution between 1985–1991, studying the presentation, modes of investigation, and evidence of hemodynamic compromise. Thirteen patients presented with intraventricular tumors during the study period. Two of the tumors were rhabdomyosarcomas, one was a myxoma, and 10 were rhabdomyomas. All patients were evaluated with two-dimensional and pulsed Doppler echocardiography and B-color imaging was undertaken in three patients. Four patients presented for elective scans to complement investigations for tuberous sclerosis, seven patients had cardiac symptoms, and two patients presented prenatally. Obstruction to intracardiac flow was present in five patients. Two patients had the tumor excised and one had an open biopsy of the tumor. One patient had an transvascular biopsy at cardiac catheter. Early detection of cardiac tumors is increasing, particularly rhabdomyomas. With fetal echocardiography, more patients should come to attention prenatally. B-color may be a useful addition in assessing cardiac tumors, aiding detection and definition of intramural lesions.

13 newborn infants with aortic coarctation were evaluated by counter-current aortographic technique. The right radial or brachial artery approach (2 cases in each group) did not give successful aortic arch imaging while the right axillary artery approach resulted in adequate imaging in each of 9 cases investigated. In 2, the axillary artery was transiently weakened but returned to normal within 24 h. No other complications were encountered. Axillary artery counter-current aortography is a safe and relatively non-invasive procedure which can be used to image the aortic arch in the newborn babies when other non-invasive diagnosis of aortic arch obstruction is tentative.

The paper recapitulates the method of analyzing stability against chatter of machine tools as it has been practised by one of the authors for many years. Several new features of the method are presented and, mainly, comments are given on the use of shock excitation for determining both the receptances of the structure and its mode shapes. The method itself consists of comparing results of cutting tests and of excitation tests for various directional orientations of the cut in the structure and of identifying the contribution of the individual modes to the resulting degree of stability.

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