High pressure X-ray photochemical studies of carbon tetrachloride: Cl 2 production and segregation Michael Pravica ⇑ , Daniel Sneed, Quinlan Smith, Ligang Bai High Pressure Science and Engineering Center (HiPSEC), Department of Physics, University of Nevada Las Vegas (UNLV), Las Vegas, NV 89154-4002, USA article info Article history: Received 26 July 2013 In final form 20 October 2013 Available online 25 October 2013 abstract We report on two experiments on carbon tetrachloride. CCl 4 was pressurized to 4.9 GPa and irradiated with 20 keV hard X-rays for 4 h and 8 h respectively. We observed a greenish yellow material form in the irradiated regions. In the second experiment, the same irradiated sample was left pressurized for 4 weeks. The irradiated regions consolidated and Raman spectra of these spots displayed strong Cl 2 lines. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Carbon tetrachloride (CCl 4 ) is a simply constructed, toxic, sp 3 - bonded, tetragonally-shaped molecule, and relatively inert inor- ganic solvent that has many industrial uses including its former wide use as a dry cleaning agent and as an etching gas for electron- ics [1,2]. We sought to examine CCl 4 as a potential candidate to produce Cl 2 via hard X-ray irradiation to further expand our reper- toire of useful simple molecule-producing-reactions – particularly in an effort to release challenging-to-load and reactive halogens (Cl 2 ,F 2 ,I 2 , Br 2 , etc.) in sealed and isolated chambers utilizing useful hard X-ray chemistry [3–7]. Current methods used to load these toxic and reactive compounds can incur considerable health risk and often contaminate scientific equipment (such as cryostats and vacuum apparatus). Loading these reactive and toxic halogens by introducing a relatively benign and inert material into the dia- mond anvil cell or other sealed chamber and then irradiating the sample to release the toxic gases would offer a tremendous advan- tage over conventional pressure bomb or cryogenic loading meth- ods. As we have successfully produced oxygen from KClO 3 [3], we reasoned that CCl 4 , which has an abundance of sp 3 bonded Cl atoms covalently bonded to carbon, might have a reasonable chance to breakdown by similar X-ray induced methods. Thus, the goal of this study was to investigate the behavior of CCl 4 under intense X-ray irradiation from a synchrotron X-ray source. 2. Experimental Two experiments were performed. The first experiment investi- gated the effects of X-ray irradiation when the sample was set at a fixed pressure. The second experiment sought to determine any time-dependent effects associated with the irradiated and pressur- ized sample. We used a symmetric-style Diamond Anvil Cell (DAC) with 250 lm thick stainless steel gaskets to pressurize and confine CCl 4 . The diamonds used each had a culet diameter of 300 lm and were low fluorescence type II quality. The sample-holding gas- ket was preindented to 50 lm thickness and a sample hole of diameter 100 lm was drilled via electric discharge machining. Li- quid CCl 4 (Burdick & Jackson spectrophotometer grade >99%) was loaded via a syringe into the gasket hole along with one ruby (for pressure measurement) and then the assembly was closed to seal the sample. No pressure-transmitting medium was used in our experiments and all experiments were performed at room temperature. The first experiment was performed at the 16 BM-D beamline of the Advanced Photon Source. Monochromatic x-rays of energy 20 keV served as the energy source. This energy was chosen based on our experience from prior experiments [7] as an energy that causes reasonably rapid decomposition in KClO 3 . At ambient tem- perature, CCl 4 exhibits four [8] (possibly five [2]) known phases (I– V) with pressure. Phase I solidifies from the liquid state near 0.13 GPa [2]. Our goal was to maintain the sample in the solid state, well above any melt line at all points of our experiment to reduce any chance of leakage. A fresh CCl 4 sample was loaded in the DAC and was pressurized to 4.9 GPa. The sample was placed in the path of a focused 30  30 lm monochromatic 20 keV X-ray beam centered on the sample for some 4 h and then the sample was translated and moved off-center and irradiated for another 8 h. Raman spectros- copy was performed on the sample (both the irradiated and unir- radiated regions) to interrogate any differences between the regions. The second experiment was conducted in the Pravica group Ra- man facility. The irradiated sample from the second experiment was left pressurized at ambient temperature for approximately 0009-2614/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cplett.2013.10.056 ⇑ Corresponding author. Fax: +1 (702)895 0804. E-mail address: pravica@physics.unlv.edu (M. Pravica). Chemical Physics Letters 590 (2013) 74–76 Contents lists available at ScienceDirect Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett