The Elusive Ketene (H2CCO) Channel in the Infrared Multiphoton Dissociation of Solid 1,3,5‐Trinitro‐1,3,5‐Triazinane (RDX)

• Published in: Chemphyschem 2020-05, Vol.21 (9), p.837-842
• Main Authors: Singh, Santosh K., La Jeunesse, Jesse, Vuppuluri, Vasant, Son, Steven F., Sun, Bing‐Jian, Chen, Yue‐Lin, Chang, Agnes H. H., Mebel, Alexander M., Kaiser, Ralf I.
• Format: Article
• Language: English
• Subjects: ab initio calculations; Channels; Decomposition; Diazomethane; Dissociation; Electronic structure; Energetic materials; Infrared lasers; infrared multiphoton dissociation; Mass spectrometry; Photoionization; RDX; Thin films
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201901202

Understanding of the fundamental mechanisms involved in the decomposition of 1,3,5‐trinitro‐1,3,5‐triazinane (RDX) still represents a major challenge for the energetic materials and physical (organic) chemistry communities mainly because multiple competing dissociation channels are likely involved and previous detection methods of the products are not isomer selective. In this study we exploited a microsecond pulsed infrared laser to decompose thin RDX films at 5 K under mild conditions to limit the fragmentation channels. The subliming decomposition products during the temperature programed desorption phase are detected using isomer selective single photoionization time‐of‐flight mass spectrometry (PI‐ReTOF‐MS). This technique enables us to assign a product signal at m/z=42 to ketene (H2CCO), but not to diazomethane (H2CNN; 42 amu) as speculated previously. Electronic structure calculations support our experimental observations and unravel the decomposition mechanisms of RDX leading eventually to the elusive ketene (H2CCO) via an exotic, four‐membered ring intermediate. This study highlights the necessity to exploit isomer‐selective detection schemes to probe the true decomposition products of nitramine‐based energetic materials. True structure: Fundamental understanding of the elementary reactions involved in the decomposition of 1,3,5‐trinitro‐1,3,5‐triazinane (RDX) is still a major challenge due to lack of identification of accurate structure of the decomposition products. For the first time, we have employed isomer‐selective photoionization mass‐spectrometry technique to probe the true structure of a decomposition product of RDX, which is observed at mass‐to‐charge ratio of 42.