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利用飞秒泵浦-探测技术结合飞行时间质谱(TOF-MS),研究了丙烯酸分子被200nm泵浦光激发到第二电子激发态(S2)后的超快预解离动力学.采集了母体离子和碎片离子的时间分辨质谱信号,并利用动力学方程对时间分辨离子质谱信号进行拟合和分析,揭示了预解离通道的存在.布居在S2激发态的分子通过快速的内转换弛豫到第一电子激发态(S1),时间常数为210fs,随后再经内转换从S1态弛豫到基态(S0)的高振动态,时间常数为1.49ps.分子最终在基态高振动态势能面上发生C-C键和C-O键的断裂,分别解离生成H2C=CH和HOCO、H2C=CHCO和OH中性碎片,对应的预解离时间常数分别约为4和3ps.碎片离子的产生有两个途径,分别来自于母体离子的解离和基态高振动态势能面上中性碎片的电离.
The ultrafast pre-dissociation kinetics of acrylic molecules excited by the pump light at 200 nm to the second electron-excited state (S2) was investigated by using the femtosecond pump-detection technique combined with time of flight mass spectrometry (TOF-MS) Ions and fragment ions, and using kinetic equations to fit and analyze the time-resolved ion mass spectrometry signals, revealing the presence of pre-dissociation channels.The molecules residing in the S2-excited state undergo rapid internal transitions The first electron-excited state (S1) has a time constant of 210 fs and then undergoes an internal transition from the relaxation of the S1 state to the high-vibrational state of the ground state (S0) with a time constant of 1.49 ps. On the CC bond and CO bond break, respectively, dissociation generated H2C = CH and HOCO, H2C = CHCO and OH neutral fragments, corresponding to the pre-dissociation time constant of about 4 and 3ps. Fragment ions produced two Pathways, respectively, from the dissociation of the parent ion and the ground state high vibration potential energy surface neutral ionization.