The gas-phase oxygen-hydrogen exchange reaction dynamics of O((3)P) + i-C3H7 (isopropyl) → H((2)S) + CH3OCH3 (acetone) was first investigated by the vacuum-ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy in a crossed beam configuration. The nascent H-atom Doppler-profile analysis shows that the average translation energy of the products and the fraction of the total available energy released as the transitional energy were determined to be 33.3 ± 1.64 kcal mol(-1) and 0.38, respectively. With the aid of the CBS-QB3 level of ab initio theory and statistical calculations, it was found that the title reaction is one of the major reaction pathways and proceeds through the formation of dynamical, short-lived addition complexes. On the basis of a systematic comparison with several exchange reactions of hydrocarbon radicals, the large variation in the fractions of translational energy release can be understood in terms of the unique geometrical features of the transition states along the reaction coordinates on the doublet potential energy surfaces.

The gas-phase radical-radical reaction dynamics of ground-state atomic oxygen [O((3)P)] with iso-propyl radicals, (CH(3))(2)CH, were investigated by applying a combination of high-resolution laser-induced fluorescence spectroscopy in a crossed-beam configuration and ab initio calculations. The nascent distributions of OH (X(2)Π: υ'' = 0) from the major reaction channel O((3)P) + (CH(3))(2)CH → C(3)H(6) (propene) + OH showed substantial internal excitations with a bimodal feature of low- and high-N'' components with neither spin-orbit nor Λ-doublet propensities. Unlike previous kinetic results, proposed to proceed only through the direct H-atom abstraction process, on the basis of the population analysis and comparison with the statistical theory, the title reaction can be described in terms of two competing mechanisms at the molecular level: direct abstraction process and indirect short-lived addition-complex-forming process with a ratio of 1.25 : 1.

This paper reports on the gas-phase radical-radical dynamics of the reaction of ground-state atomic oxygen [O((3)P), from the photodissociation of NO(2)] with secondary isopropyl radicals [(CH(3))(2)CH, from the supersonic flash pyrolysis of isopropyl bromide]. The major reaction channel, O((3)P)+(CH(3))(2)CH→C(3)H(6) (propene)+OH, is examined by high-resolution laser-induced fluorescence spectroscopy in crossed-beam configuration. Population analysis shows bimodal nascent rotational distributions of OH (X(2)Π) products with low- and high-N'' components in a ratio of 1.25:1. No significant spin-orbit or Λ-doublet propensities are exhibited in the ground vibrational state. Ab initio computations at the CBS-QB3 theory level and comparison with prior theory show that the statistical method is not suitable for describing the main reaction channel at the molecular level. Two competing mechanisms are predicted to exist on the lowest doublet potential-energy surface: direct abstraction, giving the dominant low-N'' components, and formation of short-lived addition complexes that result in hot rotational distributions, giving the high-N'' components. The observed competing mechanisms contrast with previous bulk kinetic experiments conducted in a fast-flow system with photoionization mass spectrometry, which suggested a single abstraction pathway. In addition, comparison of the reactions of O((3)P) with primary and tertiary hydrocarbon radicals allows molecular-level discussion of the reactivity and mechanism of the title reaction.

BACKGROUND The authors assessed the biologic behavior of differentiated thyroid carcinoma in patients age 70 years or older and evaluated factors that influenced long‐term survival. METHODS Among 1448 patients with differentiated thyroid carcinoma who were treated at the authors' institution over the past 60 years, 111 patients were identified who were age 70 years or older at the time of their initial diagnosis (range, 70–93 years). The authors conducted a retrospective analysis of the outcome of these 111 patients, who had a median follow‐up of 9 years (range, 2–9 years). RESULTS There were 83 female patients and 28 male patients (female to male ratio, 3:1). Fifty‐eight tumors were papillary, 46 tumors were follicular, and 7 tumors were Hürthle cell carcinoma. Eighty percent of patients presented with a thyroid mass, and 70% of tumors were pathologic stage T3 (pT3) or pT4. Lymph node disease was evident at presentation in 44% of patients, and distant metastases were documented at diagnosis in 23% of patients. Forty‐six patients underwent total thyroidectomy, and the remaining patients underwent subtotal thyroidectomy or biopsy only. Radioiodine was administered to 80 patients, and external beam radiotherapy was administered to 19 patients. The cause specific survival rates were 75%, 50%, and 50% at 5 years, 10 years, and 15 years, respectively. Multivariate analysis showed that the presence of metastases was the most important independent prognostic factor for survival. External beam radiotherapy was associated with a poorer prognosis, in that it was reserved for patients with either inoperable disease or residual disease after surgery and patients with no uptake of radioiodine. CONCLUSIONS A large proportion of thyroid tumors showed extrathyroid spread and distant metastases, which frequently were not iodine‐avid. The prevalent histologic type was papillary, often with features of poor differentiation. Thyroid carcinoma in the elderly appears to behave more aggressively, and they have a less favorable prognosis compared with younger adults. Cancer 2003;97:2736–42. © 2003 American Cancer Society. DOI 10.1002/cncr.11410