Mixed silicon carbide clusters are important components of circumstellar shells and their optical properties are fundamental for modelling the chemistry involved in the evolution of dust particles. Herein, we report the ultraviolet photodissociation (UVPD) spectrum of mass-selected Si₄C₂⁺ cations obtained in the 208–330 nm range (3.8–6.0 eV) in a quadrupole/time-of-flight tandem mass spectrometer coupled to a laser desorption source operating with a SiC rod and a broadly tuneable optical parametric oscillator laser. The UVPD spectrum is observed in the two lowest-energy fragment channels, corresponding to dominant loss of atomic Si at low energy and the rather stable Si₂C molecule at high energy. The UVPD spectrum is analyzed by quantum chemical calculations at two levels of density functional theory (CAM-B3LYP, M11) to determine the structures, energies, electronic spectra, and fragmentation energies of the lowest-energy isomers. To locate these isomers on the multidimensional potential energy surface, basin hopping is employed as global optimization approach. The UVPD spectrum is consistent with the optical absorption spectrum computed for the two lowest-energy isomers, one of which is reported for the first time.

混合的碳化硅团簇是恒星壳的重要组成部分，它们的光学特性对于模拟尘埃演化过程中涉及的化学反应至关重要。在本文中，我们报告了在四极杆/飞行时间串联质谱仪中，在208-330 nm范围内（3.8-6.0 eV）获得的质量选择的Si ₄ C ₂ ⁺阳离子的紫外光解离（UVPD）光谱。SiC棒和可广泛调谐的光学参量振荡器激光器工作的激光解吸源。在两个最低能量的碎片通道中观察到了UVPD光谱，这对应于低能量下的原子Si的主要损失和相当稳定的Si ₂C分子处于高能状态。在密度泛函理论的两个级别（CAM-B3LYP，M11）通过量子化学计算分析UVPD光谱，以确定最低能量异构体的结构，能量，电子光谱和碎片能。为了将这些异构体定位在多维势能表面上，采用盆地跳跃法作为全局优化方法。UVPD光谱与针对两种最低能量异构体计算的光吸收光谱一致，其中一个是首次报道。