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首页> 外文期刊>The Journal of Chemical Physics >SPECTRAL LINE SHAPES IN SYSTEMS UNDERGOING CONTINUOUS FREQUENCY MODULATION
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SPECTRAL LINE SHAPES IN SYSTEMS UNDERGOING CONTINUOUS FREQUENCY MODULATION

机译：进行连续频率调制的系统中的谱线形状

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The power spectrum line shapes for oscillators undergoing a continuous modulation of the vibrational frequency are investigated. It is shown that the single, sharp line normally characteristic of such systems broadens and exhibits a wealth of fine structure components. The characteristic fine structure pattern is one of decreasing amplitude and spacing. This continuous frequency modulation (CFM) effect has been examined for a series of model oscillators that includes harmonic systems with Linear and exponential variation of the frequency without amplitude damping, a harmonic system with exponential damping of both the resonant frequency and the amplitude, and a Morse oscillator whose kinetic energy is being exponentially damped. An analytic expression for the power spectrum of a harmonic oscillator whose frequency is varying linearly with time is derived. This result demonstrates that the position of the fine structure extrema depends linearly upon the initial oscillator frequency and the square root of the absolute value of the modulation rate. The peak-to-peak spacing is shown to be proportional to the square root of the absolute value of the modulation rate. It is suggested that the CFM effect is the fundamental explanation of many previous empirical observations concerning power spectra. The CFM effect for a harmonic system with an exponentially modulated frequency is very similar to that observed for linear modulation. When amplitude depression is included, there is a significant intensity decrease of many of the spectral lines. Investigation of a Morse oscillator shows that energy transfer in an anharmonic system produces a CFM effect. By assuming that the analytic result for a harmonic oscillator with a Linear modulation is transferable to the anharmonic case, an expression is obtained that relates the peak-to-peak fine structure spacing to the Morse potential parameters, the initial oscillator energy and the IVR rate coefficient. An experimental example of a CFM effect is presented by taking an NMR spectrum of H2O and HCCl3 in DCCl3 while the main B-0 field is varying with time. The CFM effect is used to extract energy transfer rate coefficients for a diatomic molecule isolated in an argon matrix at 12 K and for total IVR rate coefficients for relaxation of the N=O and O-H local modes in cis-HONO. It is also shown that instantaneous energy transfer rates in small molecules can be determined by using local frequency analysis to compute: the temporal variation of the CFM band spacings. It is concluded that line shape analysis can be effectively used as a probe of energy transfer rates. (C) 1996 American Institute of Physics. [References: 27]
机译：研究了振动频率连续调制的振荡器的功率谱线形状。结果表明，这种系统通常具有的单一尖锐线会加宽并显示出许多精细的结构部件。特征性的精细结构图案是减小幅度和间隔的一种。已针对一系列模型振荡器研究了这种连续调频（CFM）效果，这些模型振荡器包括具有线性和指数变化且无振幅阻尼的谐波系统，具有谐振频率和振幅均呈指数阻尼的谐波系统，以及摩尔斯振荡器，其动能被指数衰减。推导了频率随时间线性变化的谐波振荡器功率谱的解析表达式。该结果表明，精细结构极值的位置线性地取决于初始振荡器频率和调制率的绝对值的平方根。峰-峰间距显示为与调制率绝对值的平方根成比例。建议CFM效应是许多以前有关功率谱的经验观察的基本解释。具有指数调制频率的谐波系统的CFM效应与线性调制所观察到的非常相似。当包括振幅降低时，许多光谱线的强度显着降低。对摩尔斯振荡器的研究表明，非谐系统中的能量转移会产生CFM效应。通过假定具有线性调制的谐波振荡器的分析结果可以转移到非谐情况，可以得到一个表达式，该表达式将峰到峰的精细结构间距与莫尔斯电势参数，初始振荡器能量和IVR速率相关联系数。通过获取DCCl3中H2O和HCCl3的NMR光谱，给出了CFM效应的实验示例，而主B-0场随时间变化。 CFM效应用于提取在12 K的氩气基质中分离出的双原子分子的能量转移速率系数，以及用于在顺式HONO中弛豫N = O和O-H局部模式的总IVR速率系数。还表明，可以通过使用局部频率分析来计算小分子中的瞬时能量转移速率，以计算：CFM带间距的时间变化。结论是，线形分析可以有效地用作能量传输速率的探针。 （C）1996年美国物理研究所。 [参考：27]

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