Overlapping spectral features and new assignment of 2‐propanol in the C–H stretching region

The vibrational spectra of gaseous and liquid 2‐propanol in the C–H stretching region of 2800 ~ 3100 cm⁻¹ were investigated by polarized photoacoustic Raman spectroscopy and conventional Raman spectroscopy, respectively. Using two deuterated samples, that is, CH₃CDOHCH₃ and CD₃CHOHCD₃, the overlapping spectral features between the CH and CH₃ groups were identified. With the aid of depolarization ratio measurements and density functional theory calculations, a new spectral assignment was presented. In the gas phase, the band at 2884 cm⁻¹ was assigned to the overlapping of one CH₃ Fermi resonance mode and a CH stretching of gauche conformer. The bands at 2917 and 2933 cm⁻¹ were assigned to another two CH₃ Fermi resonance modes, but the latter includes weak contribution from CH stretching of trans conformer. The bands at 2950 and 2983 cm⁻¹ were assigned to CH₃ symmetric and antisymmetric stretching, respectively. The spectral features of liquid 2‐propanol are similar to those in the gas phase except for the blue shift of CH and the red shift of CH₃ band positions, which can be attributed to the intermolecular interaction in the liquid state. The new assignments not only clarify the confusions in previous studies from different spectral methods but also provide the reliable groundwork on spectral application of 2‐propanol in the futures. Copyright © 2014 John Wiley & Sons, Ltd.     

CH4分子ν1模拉曼诱导克尔效应谱与受激拉曼光声光谱峰形的比较

以气相甲烷分子ν₁模Q支的拉曼光谱为例，采用拉曼诱导克尔效应谱(RIKES)进行峰形测量，并将其与同时测量的受激拉曼光声光谱(PARS)的峰形进行了比较.结果表明，在pump光和Stokes光均为线偏振的情况下，两者存在着差异；在拉曼共振峰的低频端，RIKES谱强度略高；而高频端则恰好相反.从信号产生机制出发，对此进行了合理解释. 关键词： 拉曼诱导克尔效应谱 受激拉曼光声光谱 峰形     

液体的脉冲差分光声喇曼光谱

采用脉冲光声方法测量了各种有机和无机液体的受激喇曼光谱,探讨了影响这种光谱技术灵敏度的主要原因,即来自线性吸收信号的干扰,并进一步采用一种改进的方法——差分方法,消除了线性光声信号的影响,可以测量到比较弱的喇曼谱线以及浓度比较低的物质的喇曼光谱,并探讨了这种技术在痕量物质测量以及探测环境污染物质等领域中的应用前景.     

反向泵浦的受激喇曼光声光谱

An improved experiment setup for Stimulated Photoacoustic Raman Spectroscopy（PARS）was reported. The employed two laser beams,unlike general arrangement of propagating in the same direction,counterpropagated with each other. This arrangement can eliminate the limitation that the small Raman shift could not be measured with general arrangement. Therefore,this improved setup was especially useful for measuring the PARS spectrum with small Raman shift,such as the pure rotational Raman spectrum. In the experiment,taking CH4 molecules as a research object,one laser was fixed at 532. 1 nm while another tunable dye laser scanned. The PARS spectrum of CH4 molecules for the v1 ,v2 and v3 bands was recorded in the two wavelength ranges of 625-642 nm and 573-589 nm,and the results agreed well with those obtained by Spontaneous Raman Scattering（ORS）technique,confirming the validity of the improved experimental setup.     

Precise measurement of the depolarization ratio from photoacoustic Raman spectroscopy

A new method for the accurate determination of the Raman depolarization ratio is reported with an improved setup for photoacoustic Raman spectroscopy (PARS). The precise measurement is achieved by measuring the dependence of the acoustic signal intensity on the cross‐angle between the polarizations of two incident laser beams. We demonstrate this sensitive and simple method with several gaseous molecules, such as CH₄ and H₂. The measured results of depolarization ratios agree well with the theoretical values with an upper error limit of ± 0.005, which is comparable to that with polarization‐resolved CARS spectroscopy. Copyright © 2007 John Wiley & Sons, Ltd.     

反向泵浦的受激喇曼光声光谱

报道一种改进的受激喇曼光声光谱实验方法 (PhotoacousticRamanSpectroscopy ,PARS) ,该方法的主要特点是将两束激光以反向传播的方式重合 ,从而不仅克服了通常的实验方法 (两束激光通过双色镜片重合 )在测量小喇曼位移方面的限制 ,也使实验的操作更加简单 .在实验中 ,以CH4 分子为研究对象 ,一束波长为 5 3 2 .1nm的激光作为泵浦光 ,另一束可调谐激光作为探测光 (Stokes光 ) ,两束光相向作用于光声池内 ,在 62 5～ 64 2nm和 5 73～ 5 89nm得到了CH4 分子ν1 、ν2 和ν3模的PARS光谱 ,其结果与前人利用自发喇曼散射技术 (ORS)一致 ,其中喇曼活性较弱且喇曼位移较小的ν2 模的PARS光谱是新得到的     

凝聚态物质中的光声喇曼效应理论

用热弹性理论系统地分析了凝聚态物质的光声喇曼效应,分别导出了连续和脉冲激光泵浦下的光声喇曼信号表达式,并做了数值估算.     

固体中光声喇曼效应的原理特性分析

从相干喇曼放大过程出发,运用准平衡模型以及热弹理论,对固体样品中光声喇曼效应进行理论分析,导出了脉冲激光泵浦下的光声喇曼信号表达式,并做了数值估算.总结分析了固体介质中光声喇曼效应的一些特性.