Cooling dynamics of energized naphthalene and azulene radical cations
Cooling dynamics of energized naphthalene and azulene radical cations
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DOI：
10.1063/5.0147456
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发表时间：
2023-05-07
影响因子：
4.4
通讯作者：
Bull, James N. N.
中科院分区：
文献类型：
--
作者：
Lee, Jason W. L.;Stockett, Mark H. H.;Bull, James N. N.
萘和甘菊环是同分异构的多环芳烃（PAH），由于最近在金牛座分子云-1（TMC-1）中发现了取代萘，因此在天体化学背景下成为热门话题。在这里，热和光诱导的异构化，解离，和辐射冷却动力学的能量（振动热）萘（NP+）和甘菊环（AZ（+））自由基阳离子，发生在微秒到秒的时间尺度，使用低温静电离子存储环，提供“分子云在一个盒子”的条件。通过解离形成的中性粒子的冷却动力学和动能释放分布的测量，直到热离子形成后几秒钟，与快速（亚微秒）Np+可逆箭头Az（+）准平衡的建立是一致的。因此，通过C2 H2-消除的解离主要通过常见的Az（+）分解途径进行。使用耦合主方程结合高水平势能面计算[CCSD（T）/cc-pVTZ]模拟异构化、解离、复发荧光和红外冷却动力学，再现了测量趋势。数据表明，通过经常性荧光的辐射冷却，主要是通过Np+ D-0
Naphthalene and azulene are isomeric polycyclic aromatic hydrocarbons (PAHs) and are topical in the context of astrochemistry due to the recent discovery of substituted naphthalenes in the Taurus Molecular Cloud-1 (TMC-1). Here, the thermal- and photo-induced isomerization, dissociation, and radiative cooling dynamics of energized (vibrationally hot) naphthalene (Np+) and azulene (Az(+)) radical cations, occurring over the microsecond to seconds timescale, are investigated using a cryogenic electrostatic ion storage ring, affording "molecular cloud in a box" conditions. Measurement of the cooling dynamics and kinetic energy release distributions for neutrals formed through dissociation, until several seconds after hot ion formation, are consistent with the establishment of a rapid (sub-microsecond) Np+ reversible arrow Az(+) quasi-equilibrium. Consequently, dissociation by C2H2-elimination proceeds predominantly through common Az(+) decomposition pathways. Simulation of the isomerization, dissociation, recurrent fluorescence, and infrared cooling dynamics using a coupled master equation combined with high-level potential energy surface calculations [CCSD(T)/cc-pVTZ], reproduce the trends in the measurements. The data show that radiative cooling via recurrent fluorescence, predominately through the Np+ D-0