通过分子内振动能量重新分布，在6550厘米⁻¹处三氟丙炔旋转光谱的运动变窄。

Douglass Kevin O, Dian Brian C, Brown Gordon G, Johns James E, Nair Pradeep M, Pate Brooks H

Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, USA.

J Chem Phys. 2004 Oct 8;121(14):6845-54. doi: 10.1063/1.1780164.

We present the basic principles of dynamic rotational spectroscopy for the highly vibrationally excited symmetric top molecule trifluoropropyne (TFP,CF3CCH). Single molecular eigenstate rotational spectra of TFP were recorded in the region of the first overtone of the nu(1) acetylenic stretching mode at 6550 cm(-1) by infrared-pulsed microwave-Fourier transform microwave triple resonance spectroscopy. The average rotational constant (B) of the highly vibrationally mixed quantum states at 6550 cm(-1) is 2909.33 MHz, a value that is 40 MHz larger than the rotational constant expected for the unperturbed C-H stretch overtone (2869.39 MHz). The average rotational constant and rotational line shape of the molecular eigenstate rotational spectra are compared to the distribution of rotational constants expected for the ensemble of normal-mode vibrational states at 6550 cm(-1) that can interact by intramolecular vibrational energy redistribution (IVR). The normal-mode population distribution at 6550 cm(-1) can be described using a Boltzmann distribution with a microcanonical temperature of 1200 K. At this energy the rotational constant distribution in the normal-mode basis set is peaked at about 2910 MHz with a width of about 230 MHz. The distribution is slightly asymmetric with a tail to the high end. The experimentally measured dynamic rotational spectra are centered at the normal-mode distribution peak; however, the spectral width is significantly narrower (40 MHz) than normal-mode ensemble width (230 MHz). This reduction of the width, along with the Lorentzian shape of the eigenstate rotational spectra when compared to the Gaussian shape of the calculated ensemble distribution, illustrates the narrowing of the spectrum due to IVR exchange. The IVR exchange rate was determined to be 120 ps, about ten times faster than the rate at which energy is redistributed from the v=2 level of the acetylenic stretch.

我们介绍了用于高振动激发对称陀螺分子三氟丙炔（TFP，CF3CCH）的动态旋转光谱的基本原理。通过红外脉冲微波 - 傅里叶变换微波三重共振光谱，在6550 cm⁻¹处的ν(1)炔烃伸缩模式的第一泛音区域记录了TFP的单分子本征态旋转光谱。在6550 cm⁻¹处高振动混合量子态的平均转动常数（B）为2909.33 MHz，该值比未受扰动的C - H伸缩泛音预期的转动常数（2869.39 MHz）大40 MHz。将分子本征态旋转光谱的平均转动常数和转动线形与在6550 cm⁻¹处可通过分子内振动能量重新分布（IVR）相互作用的简正模式振动态系综预期的转动常数分布进行了比较。6550 cm⁻¹处的简正模式布居分布可以用具有1200 K微正则温度的玻尔兹曼分布来描述。在这个能量下，简正模式基组中的转动常数分布在约2910 MHz处达到峰值，宽度约为230 MHz。该分布略微不对称，高端有一个尾巴。实验测量的动态旋转光谱以简正模式分布峰值为中心；然而，光谱宽度明显比简正模式系综宽度（230 MHz）窄（40 MHz）。与计算的系综分布的高斯形状相比，这种宽度的减小以及本征态旋转光谱的洛伦兹形状，说明了由于IVR交换导致光谱变窄。IVR交换率确定为120 ps，比炔烃伸缩v = 2能级的能量重新分布速率快约十倍。