Pressure Induced Reactivity of Solid CO by FTIR Studies

Abstract

The pressure induced reactivity of carbon monoxide was investigated in a wide temperature range (100-400 K) completely avoiding any irradiation of the sample with visible or higher frequency light. FTIR spectroscopy was employed to monitor the reaction and infrared sensors for measuring the pressure. With this approach we have been able to separate the effects of the three variables (P, T and hnu) that establish the conditions for the occurrence of the chemical reaction. A new instability boundary, not affected by the photoactivation of the reaction, is provided. The reaction has been studied in three different crystal phases (epsilon, delta, and beta), but the small differences in the reaction products are ascribable to the temperature changes rather than to the crystalline arrangement. For T<300 K the analysis of the IR spectra reveals the formation of an extended amorphous material formed, according to the vibrational assignment and to the kinetic data, by polycarbonyl linear chains containing a large amount of anhydride groups. For T>or=300 K the formation of carbon dioxide and epoxy rings, and the simultaneous decrease of carbonyl species, let suppose a decarboxylation of the extended solid product. Once exposed to the atmosphere, the reaction product readily and irreversibly reacts with water giving rise to carboxylic groups.

Controlling the Bonding and Band Gaps of Solid Carbon Monoxide with Pressure

“…Our structural searches give infinitely long chains, which we expect to be the most stable forms. In the polymerization process, the starting molecular structure contains head-to-tail disorder, and only short polycarbonyl chains tend to form, separated by C-O-C bonds, and the connecting parts form anhydride groups as suggested by recent experiments [12].…”

“…Pressure-induced polymerization of molecular crystals results in materials with entirely new electronic, optical, and physical properties [1,2]. CO is one of the most extensively studied molecular crystals [3][4][5][6][7][8][9][10][11][12]. Studies of polymerization of CO are motivated by the desire to understand the fundamental physics and chemistry of geological and planetary processes, where CO is present, and to search for new materials [13] exhibiting properties such as ''high energy density'' [10] and ''superhardness'' [14,15].…”

“…Molecular phases of CO and N 2 become unstable at high pressures because structures with single and double bonds are in general denser. Polymeric CO is also expected to be a good candidate high-energy-density material, as considerable energy is released on decomposition into C and CO 2 [10][11][12]. So far, only amorphous polymeric CO has been found in high pressure experiments.…”

“…Subsequent investigations have concluded that the polymer is based on lactone esters with rings closed by C ¼ C bonds [10,11]. Ceppatelli et al [12] investigated the effects of pressure and irradiation and showed that the reaction mechanisms are highly temperature dependent: the amorphous material produced at low temperature (< 300 K) is formed from polycarbonyl chains containing anhydride groups [R-ðC ¼ OÞ-O-ðC ¼ OÞ-R 0 ], while CO 2 and epoxy rings are formed at temperatures ! 300 K.…”

“…The calculated molecular dissociation pressure leading to cubic gauche N is about 56 GPa [20] and 20-25 GPa for the -and -cristobalite-like structures of CO 2 [26]. CO polymerizes at very low pressures and is sensitive to light [5,8,10,12], while polymerization of N 2 and CO 2 is observed at much higher pressures of 110-130 GPa in N 2 [15] and 40-80 GPa [14,27,28]…”