Upon either photolysis or pyrolysis, carbonyl azide can eliminate molecular nitrogen along with the formation of isocyanate. Though two different pathways (namely stepwise versus concerted) have been proposed, the detailed decomposition mechanism is still elusive to date. Herein, we have employed combined electronic structure calculations and nonadiabatic dynamics simulations to study the radiationless deactivation and rearrangement mechanisms of FC(O)N₃ in the S₃, S₂, S₁, and S₀ states in an argon matrix. On the basis of QM(CASPT2)/MM calculations, we found that, upon 193 nm irradiation, the excited-state decay of FC(O)N₃ from the S₃ state via S₂ and S₁ to the S₀ state is an ultrafast process and could be completed within 100 fs, and a subsequent Curtius rearrangement occurs in the period of ∼300 fs; the elimination of N₂ and the formation of fluorocarbonyl nitrene FC(O)N could take place in both S₁ and S₀ states rather than in higher excited states; the isomerization from FC(O)N to FNCO involves a stepwise mechanism and could only be found in the S₀ state. This mechanistic scenario has been verified by both electronic structure calculations and full-dimensional trajectory-based “on the fly” QM(CASPT2)/MM nonadiabatic dynamics simulations. Finally, the currently calculated results provide important mechanistic insights for similar carbonyl azides.

中文翻译：

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氟羰基叠氮化物FC（O）N _3的光诱导库里斯重排：QM / MM非绝热动力学模拟†

通过光解或热解，羰基叠氮化物可以消除分子氮，并形成异氰酸酯。尽管已经提出了两种不同的途径（即逐步和协调的途径），但是迄今为止，详细的分解机制仍然难以捉摸。在本文中，我们采用了结合的电子结构计算和非绝热动力学模拟来研究氩矩阵中S ₃，S ₂，S ₁和S ₀态的FC（O）N ₃的无辐射失活和重排机理。根据QM（CASPT2）/ MM计算，我们发现，在193 nm照射下，FC（O）N ₃的激发态从S ₃衰变。状态通过小号₂和S ₁到S ₀的状态是一超快过程，并且可以为100fs内完成，并且在约300个飞秒的期间发生的后续Curtius重排; N ₂的消除和氟羰基亚硝基FC（O）N的形成可以在S ₁和S _0两种状态下发生，而不是在高激发态下发生。从FC（O）N到FNCO的异构化涉及一个逐步机理，并且只能在S _0中发现状态。这种机械方案已通过电子结构计算和基于全轨迹的“动态” QM（CASPT2）/ MM非绝热动力学仿真得到了验证。最后，当前计算的结果为类似的羰基叠氮化物提供了重要的机理见解。