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The reaction between atomic carbon and acetylene has been investigated using complementary crossed molecular beam techniques. Differential cross sections have been obtained for the reactions of both ground and excited carbon atoms, C(³P[sub J], ¹D[sub 2])+ C[sub 2]H[sub 2](X ¹Σ[sup +, sub g], in experiments conducted with continuous supersonic beams, mass spectrometric detection, and time-of-flight analysis at a relative translational energy of 29.3 kJmol[sup -1]. The reaction C(³P[sub J]) + C[sub 2]H[sub 2](X ¹Σ[sup +, sub g]) has been found to lead to C[sub 3]H+H and C[sub 3]+H[sub 2] products in comparable amounts. Both H and H[sub 2] elimination pathways are found to proceed through the formation of a C[sub 3]H[sub 2] long-lived intermediate complex whose lifetime may be comparable to its rotational period. The spin-forbidden H[sub 2] elimination channel is attributed to the occurrence of intersystem-crossing between the triplet and singlet manifolds of the C[sub 3]H[sub 2] potential-energy surfaces. The reaction C(¹D[sub 2])+C[sub 2]H[sub 2](X ¹Σ[sup +, sub g]) has been found to lead to formation of C[sub 3]H+H, with a C[sub 3]H center-of-mass angular distribution strongly forward peaked, indicating a short-lived intermediate complex. Integral cross sections have been obtained for the C(³P[sub J]j) + C[sub 2]H[sub 2] (X &sup1Σ[sup +, sub g]) → C[sub 3] H + H(²S[sub ½]) reaction in experiments conducted with pulsed, supersonic molecular beams in the range of relative translational energies E[sub T]=0.38 -25.5 kJ mol[sup -1], the H(²S[sub ½) product being detected by laser-induced fluorescence. The reaction has been found to be without a barrier, relative integral cross sections being proportional to (Er)[sup -0.80&plumsn;0.03] below E[sub T]=10 kJmol[sup -1]. These findings provide direct evidence that the C(³P[sub J]) +C[sub 2]H[sub 2] reaction can occur under... [ABSTRACT FROM AUTHOR]

The 1960s saw the emergence of plastic as an indispensable component in various fields, including art and design. Acrylonitrile-butadiene-styrene (ABS) is widely used by artists and designers for a range of applications including sculptures and decorative pieces. Consequently, the necessity to conserve ABS from deterioration is a crucial issue in the field of cultural heritage preservation. Many studies have highlighted the criticality of the stability of the polybutadiene component when exposed to light. We propose a new multimodal spectroscopic approach to assess the conservation status of plastic design objects. This non-destructive approach combines correlative Brillouin and Raman micro-spectroscopy (BRaMS), external reflection IR spectroscopy and portable NMR relaxometry. BRaMS is a novel non-destructive technique in the field of heritage conservation, allowing simultaneous monitoring of chemical and mechanical changes occurring at the sample surface. The present study focused on photochemically aged LEGO® bricks made of ABS and aimed to i) correlate chemical and mechanical changes induced by light exposure and ii) introduce a surface degradation index (SDI), measurable in situ by external reflection IR spectroscopy, to assess the state of conservation of plastic artefacts. Finally, non-invasive investigations were carried out on real design objects using the MObile LABoratory (MOLAB) platform.