Aspects of the detection, monitoring and activation of methane and other hydrocarbons

Spectroscopic studies have been pursued with the aim of identifying infrared laser lines capable of being selectively absorbed by CH4, for use in natural gas detection systems and also with the aim of identifying reaction intermediates in some recently discovered C-H photo-activation reactions. High resolution (0.06 cm-1) infrared spectra of CH4, C2H6 and n-C4H10 were recorded using a Nicolet 7199 F.t.i.r. spectrometer and overlaps between CH4 absorptions and known laser lines identified enabling calculation of differential absorption coefficients between absorbed laser lines and reference laser lines for all three gases. A previously reported pair of He/Ne laser lines at 2947.91 cm-1 (3.3933 μm^-1; absorbed) and 2948.80 cm^-1 (3.3912 μm; reference) was confirmed as suitable for CH4 detection and a new pair of CO laser lines at 1263.29 cm-1 (7.9159 μm^-1; absorbed) and 1266.19 cm^-1 (7.8977 μm; reference) was identified as providing the basis for a CH4 detection system. The photochemistry of complexes of general formula [M(η5-C5R5)(CO)2] (M = Ir, Rh, Co; R = H, Me) together with [Ir(η5-C9H7)(CO)2] and [Ir(η5-C5H5)(CO)(H)2] was investigated in a variety of frozen gas matrices (including CH4, CD4, Ar, N2 12CO, 13CO and C2H4) at cryogenic temperatures (ca. 12K). Photo-generated species were identified mainly by their infrared-active CO- and IrH-stretching modes, together with isotopic labelling and CO energy-factored force-field fitting. Photo-activation of CH4 was observed for [M(η5-C5R5)(CO)2] (M = Ir, Rh; R = H, Me) affording [M(η5C5R5)(CO)(CH3)(H)], probably via dissociative CO loss, as demonstrated by the production of [M(η5C5H5)(CO)] in Ar matrices. Additional photoproducts were thought to possibly be CH4 complexes [M(η5-C5R5)(CO).CH4]. CH4 photo-activation was also observed for [Ir(η5-C5H5)(CO)(H)2], probably via initial reductive elimination of H2 to form [Ir(η5-C5H5)(CO)], which was detected in Ar matrices. [Ir(η5-C9H7)CO)2] was found to activate CH4 producing [Ir(η5-C9H7)(CO)(CH3)(H)] on photolysis, but the mechanism was less clear. The cobalt complexes did not activate CH4 at 12K, but weak bands were detected possibly assignable to CH4 complexes. Photolysis of all complexes studied in N2 matrices, with the exception of [Ir(η5-C5Me5)(CO)2], afforded monocarbonyl dinitrogen complexes, probably via CO or H2 loss as the primary photoprocess. Photolysis in CO matrices led to associative reactions possibly involving ring-slippage,