Infrared absorption of gaseous ClCS detected with time-resolved Fourier-transform spectroscopy.
A transient infrared absorption spectrum of gaseous ClCS was detected with a step-scan Fourier-transform spectrometer coupled with a multipass absorption cell. ClCS was produced upon irradiating a flowing mixture of Cl2CS and N2 or CO2 with a KrF excimer laser at 248 nm. A transient band in the region of 1160-1220 cm-1, which diminished on prolonged reaction, is assigned to the C-S stretching (nu1) mode of ClCS. Calculations with density-functional theory (B3P86 and B3LYP/aug-cc-pVTZ) predict the geometry, vibrational wave numbers, and rotational parameters of ClCS. The rotational contour of the spectrum of ClCS simulated based on predicted rotational parameters agrees satisfactorily with experimental observation; from spectral simulation, the band origin is determined to be at 1194.4 cm-1. Reaction kinetics involving ClCS, CS, and CS2 are discussed.
Observation of CH4 (v2=1 or v4=1) in the reaction Cl+CH4 with time-resolved Fourier-transform infrared absorption spectroscopy
The reaction Cl(2P)+CH4 was initiated on laser irradiation of a flowing mixture containing Cl2, CH4, and Ar at 355 nm; reaction products were monitored with a step-scan time-resolved Fourier-transform absorption spectrometer coupled with a multipass absorption cell. Not only loss of CH4 but also production of HCl, CH3Cl, highly rotationally excited CH4 [designated as CH4(J*)], and vibrationally excited CH4 (v2=1 or v4=1), designated as CH4(v*), was observed after laser irradiation. Absorption lines of CH4(J*) and CH4(v*) are assigned according to published spectral parameters. Rates of formation and decay of CH4(v*) are derived on fitting observed temporal profiles with a simple kinetic model. A bimolecular rate coefficient for formation of CH4(v*) is determined to be (1.1±0.2)×10−14 cm3 molecule−1 s−1, nearly identical to that reported for the reaction Cl+CH4. Experimental evidence indicates that the reaction Cl+CH4 is rate determining to formation of CH4(v*). CH4(v*) is likely produced through energy tr...
Taphonomy of Isisfordia duncani specimens from the Lower Cretaceous (upper Albian) portion of the Winton Formation, Isisford, central-west Queensland
Taphonomic analysis of fossil material can benefit from including the results of actualistic decay experiments. This is crucial in determining the autochthony or allochthony of fossils of juvenile and adult Isisfordia duncani, a basal eusuchian from the Lower Cretaceous (upper Albian) distal-fluvial-deltaic lower Winton Formation near Isisford. The taphonomic characteristics of the I. duncani fossils were documented using a combination of traditional taphonomic analysis alongside already published actualistic decay data from juvenile Crocodylus porosus carcasses. We found that the I. duncani holotype, paratypes and referred specimens show little signs of weathering and no signs of abrasion. Disarticulated skeletal elements are often found in close proximity to the rest of the otherwise articulated skeleton. The isolated and disarticulated skeletal elements identified, commonly cranial, maxillary and mandibular elements, are typical of lag deposits. The holotype QM F36211 and paratype QM F34642 were classified as autochthonous, and the remaining I. duncani paratypes and referred specimens are parautochthonous. We propose that I. duncani inhabited upper and lower delta plains near the Eromanga Sea in life. Their carcasses were buried in sediment-laden floodwaters in delta plain overbank and distributary channel deposits. Future studies should refer to I. duncani as a brackish water tolerant species.