Experimental Studies for structure and Isomerization Dynamics of Triplet Acetylene

用汞光敏化技术产生了正常乙炔和氢化物乙炔的三重态，并用近红外二极管激光光谱对其进行了探测。在7300-7500 cm^-1的多普勒极限分辨率下观察到一千条吸收谱线，并归属于电子从^3B_2态到d^3A_2态的跃迁。在不对称(K-)倍增中出现的两个等价质子或重离子引起的强度变化清楚地表明，三重态乙炔的结构是顺式弯曲的。能带起源和转动常数与以前的低分辨研究和最近的理论结果符合得很好。测定了C_2H_2、C_21-D和C_2D_2的自旋旋转和自旋-自旋相互作用常数，并对三重态的动力学前景进行了研究，以揭示三重态和单重态之间的相互作用。利用半导体激光动力学光谱和脉冲汞敏化相结合的方法测量了其沿时间轴的瞬时吸收分布。用Stern-Volmer分析外推了无碰撞条件下的寿命。C_2H_2的^3B_2态的自然寿命约为4x10^-^5秒。它与旋转态和自旋态(F_1、F_2、F_3)无关。然而，C_2D_2的寿命是C_2H_2的3倍。这些结果将是理解弯曲三重态激发态到线性单重态基态的内部转换机制的关键。

The triplet states of normal and deuteride acetylene were generated by mercury photo-sensitized techniques and were detected by using near infrared diode laser spectroscopy. A thousand of absorption lines were observed in Doppler limited resolution in the 7300-7500 cm^-^1 and were assigned to the electronic transition from a ^3B_2 to d ^3A_2 state. The intensity alternation due to two equivalent protons or deuterons appeared in the asymmetry (K-)doubling clearly showed that the structure of the triplet acetylene is cis-bent. The band origin and rotational constants agrees well to a previous low resolution study and recent theoretical results. Spin rotation and spin-spin interaction constants determined are consistent among C_2H_2. C_21-D and C_2D_2.A kinetic future of the triplet state was also studied in order to reveal the interaction between the triplet and singlet states. The transient absorption profiles along the time axis were measured by using diode laser kinetic spectroscopy combined with a pulsed mercury photo-sensitized method. The lifetime at the collision free condition was extrapolated by Stern-Volmer analysis. The natural lifetime of a ^3B_2 state of C_2H_2 is about 4xl0^-^5 second. which is independent to the rotational states and spin states(F_1.F_2, F_3). However, the lifetime of C_2D_2 is three times longer than that of C_2H_2. These results would be a key point for understanding the internal conversion mechanism from the bent triplet excited state to the linear singlet ground state.