RESUMEN
A large experimental spectroscopic data set sensitive to the cubic anharmonic potential energy surface (PES) of methyl fluoride has been compiled from the literature for six symmetric and asymmetric top isotopomers of methyl fluoride: 12CH3F, 13CH3FF, 12CD3F, 13CD3F, 12CHD2F and 12CH2DF. This empirical data set has been used to critically assess the best available literature ab initio cubic force field and various 'improved' theoretical force fields. A perturbation-resonance approach to the calculation of the observables from the force constants has been utilized and existing PESs were found to reproduce the data poorly. The careful treatment required for the correct theoretical reproduction of empirical spectroscopic constants arising from highly correlated least-squares fits to the original data is discussed. A new fit to the data has been performed (optimising 19 of the 38 cubic force constants) resulting in a much improved PES. The latter has been used to predict currently unknown spectroscopic constants for the least well-characterised isotopomer 12CH2DF. The prospects for a future empirical determination of the complete cubic force field of methyl fluoride are discussed and new data most likely to yield new information on the PES identified.
Asunto(s)
Hidrocarburos Fluorados/química , Espectrofotometría Infrarroja/métodos , Fenómenos Químicos , Química Física , Hidrocarburos Fluorados/análisis , Análisis de los Mínimos Cuadrados , Modelos TeóricosRESUMEN
Results of a high-resolution infrared study of the spectroscopy of monodeuterated methyl fluoride, CH(2)DF, are reported for the first time. Spectra ranging from 500 to 3300 cm(-1) have been obtained and cover all the fundamental bands at resolutions down to 0.005 cm(-1). The two lowest energy fundamentals, the nu(5) and nu(6) bands, have been analyzed in detail. Since the molecule has C(s) symmetry, in principle both these bands are AB hybrids, since they belong to the irreducible representation A'. However, it was found that both are almost pure A-type bands. A total of 597 A-type lines of the nu(5) band and 619 A-type lines of the nu(6) band have been assigned. Vibrational and rotational spectroscopic constants have been determined by least-squares fitting to the data. An improved band center for nu(7) is also reported. Copyright 2001 Academic Press.
RESUMEN
It is 150 years since Sir Richard Owen announced the former existence of large flightless ostrich-like birds in New Zealand based on a fragment of femur presented to him in England. Numerous studies of this extinct group of giant birds, now known by the Polynesian (plural) name 'moa', have provided much information about their effects on the flora, their recent extinction, and the evolutionary history of New Zealand and its endemic biota. Significant revision of moa taxonomy and ecology continues, and recent molecular phylogenetic analyses have stimulated new hypotheses about moa evolution.
RESUMEN
Alien plants and animals are of major economic and conservation significance in New Zealand. Plant introductions have averaged 11 species per year since European settlement in /840, and distinctive landscapes are being increasingly altered by weeds. Many introduced animals act as disease vectors or threaten native biota. Recent studies of introduced wasps show adverse effects on honey-eating and insectivorous birds. Introduced possums are now known to prey on eggs and nestlings of native birds in addition to their impact on native forests and transmittal of bovine tuberculosis. Research is increasingly focused on finding effective methods of biocontrol.
