Markus Behnke

Fast analysis of gases in the submillimeter∕terahertz with “absolute” specificity

A submillimeter∕terahertz point detector for gas monitoring and quantification is described. It is based upon the fast (∼15GHz∕s) sweeping of high spectral purity (<1∕107), high brightness (∼1014K) microwave sources and a scanning electronic reference for frequency measurement. This approach can quantify the complex rotational spectrum of gases at a rate of ∼105 spectral resolution elements∕second at high signal to noise. This resolution and the uniqueness of Doppler limited rotational spectra provide “absolute” specificity and “zero” false alarm rates even in complex mixtures. Moreover, the small size, low power consumption, and the potential of very low cost make this approach attractive for a number of important applications.

The Detection oftert-Butylthiosulfoxylic Acid,t-BuSSOH, and 1-Oxatrisulfane, HSSOH, in the Gas Phase - Experimental Results and Ab Initio Calculations

Flash vacuum pyrolysis (FVP) of tert-butylthiosulfinic acid S-tert-butylester, t-BuS(O)St-Bu, at a temperature of 500 °C and a pressure of 0.07 hPa leads to the formation of tert-butylthiosulfoxylic acid, t-BuSSOH (1), and 2-methylpropene as byproduct. 1 has been identified in the gas phase by its IR absorption bands at ν(OH) = 3598 cm–1, δ(SOH) = 1149 cm–1 and ν(SO) = 718 cm–1. At higher temperatures (700 °C) the elimination of a second mole of 2-methylpropene and the shift of ν(SO) to higher wavenumbers (750 cm–1) indicate the formation of 1-oxatrisulfane, HSSOH. Different sulfenic acids RSOH (R = Me, i-Pr, t-Bu) were synthesized by FVP in order to study the influence of the substituent R on the vibrational wavenumbers ν(OH), ν(SO) and δ(SOH) observed in the gas phase. The strongest effect results for δ(SOH) leading to a decrease by 6 wavenumbers if the methyl group is substituted by a tert-butyl group. The assignment of the experimental wavenumbers has been supported by theoretical values obtained from ab initio calculations at the MP2(fc)/6-311G** level. Furthermore, the theoretical studies show that of all compounds RS2OR′ (R = R′ = H, Me; R = Me (H), R′ = H (Me)) the unbranched chain isomers RSSOR′ are energetically favored over the branched chain isomers. Relaxed potential energy surface scans at the MP2(fc)/6-311G** level have been carried out to study the rotational isomers of the branched molecules RS(Y)XR′ (R = R′ = H, Me; R = Me (H), R′ = H (Me); X = O (S), Y = S (O)). Of the three conformations (+)syn-clinal, (–)syn-clinal, and anti-periplanar resulting from molecular model considerations only the two latter ones correspond to local minima on the calculated potential curve. The (–)syn-clinal conformation is slightly favored for all other constitutional isomers except for HS(O)SH and MeS(O)SH, which prefer the anti-periplanar conformation.