Criegee intermediates (i.e., carbonyl oxides with two radical sites) are known to be important atmospheric reagents; however, our knowledge of their reaction kinetics is still limited. Although experimental methods have been developed to directly measure the reaction rate constants of stabilized Criegee intermediates, the experimental results cover limited temperature ranges and do not completely agree well with one another. Here we investigate the unimolecular reaction of acetone oxide [(CH₃)₂COO] and its bimolecular reaction with H₂O to obtain rate constants with quantitative accuracy comparable to experimental accuracy. We do this by using CCSDT(Q)/CBS//CCSD(T)-F12a/DZ-F12 benchmark results to select and validate exchange-correlation functionals, which are then used for direct dynamics calculations by variational transition state theory with small-curvature tunneling and torsional and high-frequency anharmonicity. We find that tunneling is very significant in the unimolecular reaction of (CH₃)₂COO and its bimolecular reaction with H₂O. We show that the atmospheric lifetimes of (CH₃)₂COO depend on temperature and that the unimolecular reaction of (CH₃)₂COO is the dominant decay mode above 240 K, while the (CH₃)₂COO + SO₂ reaction can compete with the corresponding unimolecular reaction below 240 K when the SO₂ concentration is 9 × 10¹⁰ molecules per cubic centimeter. We also find that experimental results may not be sufficiently accurate for the unimolecular reaction of (CH₃)₂COO above 310 K. Not only does the present investigation provide insights into the decay of (CH₃)₂COO in the atmosphere, but it also provides an illustration of how to use theoretical methods to predict quantitative rate constants of medium-sized Criegee intermediates.

已知Criegee中间体（即具有两个自由基位点的羰基氧化物）是重要的大气试剂。但是，我们对它们的反应动力学的了解仍然有限。尽管已经开发了直接测量稳定的Criegee中间体的反应速率常数的实验方法，但是实验结果涵盖了有限的温度范围，并且彼此之间并不完全吻合。在这里，我们研究了丙酮氧化物[（CH ₃）₂ COO]的单分子反应及其与H _2的双分子反应。O获得速率常数，其定量精度可与实验精度媲美。为此，我们使用CCSDT（Q）/ CBS // CCSD（T）-F12a / DZ-F12基准测试结果来选择和验证交换相关函数，然后将其用于基于变态状态理论的直接动力学计算中，曲率隧穿以及扭转和高频非谐性。我们发现隧穿在（CH ₃）₂ COO的单分子反应及其与H ₂ O的双分子反应中非常重要。我们证明（CH ₃）₂ COO的大气寿命取决于温度，并且（（ CH ₃）₂COO是高于240 K的主要衰减模式，而当SO ₂浓度为9×10 ¹⁰分子/立方厘米时，（CH ₃）₂ COO + SO ₂反应可与相应的240 K以下的单分子反应竞争。我们还发现，对于310 K以上的（CH ₃）₂ COO的单分子反应，实验结果可能不够准确。本研究不仅为深入了解大气中（CH ₃）₂ COO的衰减提供了见解，而且还提供了有关如何使用理论方法来预测中型Criegee中间体定量速率常数的说明。