苯乙炔分子电子激发态超快动力学研究

Ultrafast dynamics of electron excited states of phenylacetylene

采用飞秒时间分辨质谱技术结合飞秒时间分辨光电子影像技术研究了苯乙炔分子电子激发态超快非绝热弛豫动力学.用235 nm光作为泵浦光,将苯乙炔分子激发到第二激发态S2,用400 nm光探测激发态的演化过程.时间分辨的母体离子的变化曲线用指数和高斯函数卷积得到不同的两个组分,一个是超快衰减组分,时间常数为116 fs,一个是慢速组分,时间常数为106 ps.通过分析时间分辨的光电子影像得到光电子动能分布,结合时间分辨光电子能谱数据发现,时间常数为116 fs的快速组分反映了S2态向S1态的内转换过程.实验还表明S1态通过内转换被布局后向T1态的系间窜跃过程为重要的衰减通道.本工作为苯乙炔分子S2态非绝热弛豫动力学提供了较清晰的物理图像.

Interaction of light with matter has always been important in the field of natural science.Particularly,the ultrafast radiationless relaxation induced by UV light of molecular electronic excited states accompanied by ultrafast energy transfer plays an important role in the natural photophysical,photochemical and biological reactions.Generally,the molecular electronic excited state can be deactivated through a variety of decay channels,including dissociation,isomerization,internal conversion,intersysterm crossing,vibrational energy redistribution,and autoionization.This complexity of relaxation channels brings about a wide variety of deactivation mechanisms.The ultrafast nonadibatic relaxation dynamics of the excited state of phenylacetylene is studied by using femtosecond time-resolved photoelectron imaging and femtosecond time-resolved mass spectrometry.The first excited state S2 of phenylacetylene is excited by 235 nm pump light,and the excited state deactivation process is detected by 400 nm probe light.The time-dependent curves of parent ions include two exponential curves.One is the fast component with a time constant of 116 fs,and the other is the slow component with a time constant of 106 ps.The time-resolved photoelectron kinetic energy distribution is obtained from the time-resolved photoelectron images.Combined with the time-resolved photoelectron spectroscopy data,the fast component with a time constant of 116 fs is found to reflect the internal conversion process from S2 state to S1 state.The experimental results also show that S1 state is arranged by internal conversion,and the inter system jump process to T1 state is an important attenuation channel.This work provides a clearer physical picture for S1 state nonadibatic relaxation dynamics of phenylacetylene.