偏振调制泵浦-探测瞬态光谱研究NADH激发态的各向异性弛豫
Anisotropic relaxation in NADH excited states studied by polarization-modulation pump-probe transient spectroscopy
AI总结：
本研究采用偏振调制泵浦-探测瞬态光谱等方法，结合理论模型，探究水-乙醇溶液中NADH激发态的各向异性弛豫与旋转扩散，明确了振动弛豫、旋转扩散时间及跃迁偶极矩旋转参数与乙醇浓度等的关联。
摘要：
我们展示了水-乙醇溶液中生物辅酶NADH第一电子激发态内快速各向异性弛豫和旋转扩散的实验与理论研究结果。实验采用一种新型偏振调制瞬态方法和荧光偏振光谱进行。为解释实验结果，基于Born-Oppenheimer近似，建立了一个以跃迁偶极矩的标量和矢量性质描述各向异性弛豫的模型。所得结果表明，在100 fs泵浦激光脉冲激发下，NADH中各向异性振转弛豫的动力学可由一个处于2–15 ps范围的单一振动弛豫时间$τ_v$和一个处于100–450 ps范围、取决于乙醇浓度的单一旋转扩散时间$τ_r$表征。确定并分析了时间$τ_v$和$τ_r$对溶液极性（静态介电常数）和黏度的依赖关系。还从实验确定并分析了一个重要参数$\langle P_2(\cosθ(t))\rangle$的极限值随乙醇浓度的变化，该参数描述振动弛豫过程中跃迁偶极矩的旋转。
英文摘要：
We present the results of experimental and theoretical studies of fast anisotropic relaxation and rotational diffusion in the first electron excited state of biological coenzyme NADH in water-ethanol solutions. The experiments have been carried out by means of a novel polarization-modulation transient method and fluorescence polarization spectroscopy. For interpretation of the experimental results a model of the anisotropic relaxation in terms of scalar and vector properties of transition dipole moments and based on the Born-Oppenheimer approximation has been developed. The results obtained suggest that the dynamics of anisotropic rovibronic relaxation in NADH under excitation with 100~fs pump laser pulses can be characterised by a single vibration relaxation time $τ_v$ laying in the range 2--15~ps and a single rotation diffusion time $τ_r$ laying in the range 100--450~ps a subject of ethanol concentration. The dependence of the times $τ_v$ and $τ_r$ on the solution polarity (static permittivity) and viscosity has been determined and analyzed. Limiting values of an important parameter $\langle P_2(\cosθ(t))\rangle$ describing the rotation of the transition dipole moment in the course of vibrational relaxation has been determined from experiment as function of the ethanol concentration and analyzed.
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