Diode Laser Spectroscopy of Van Der Waals Complex Molecule

对弱束缚分子的详细研究很重要，因为可以从这种复合物的光谱学中获得关于长范围分子间力性质的定性知识。傅里叶变换微波光谱结合脉冲喷嘴技术对弱有界分子进行了广泛的研究。除了微波区的旋转光谱外，分子配合物的高分辨率红外研究也很有意义，因为可以直接知道弱束缚键的动力学性质，如振动预解离和大振幅运动。在本研究中，我们开发了用于检测弱结合分子配合物的中红外二极管激光光谱，如范德华配合物和氢键配合物。利用脉冲喷嘴技术在超音速自由膨胀射流中生成弱有界配合物，并直接观察到配合物的红外吸收光谱。从二极管激光源发出的可调谐红外辐射被准直并进入高真空分子光束室。激光通过两个近似平行的反射镜，与分子束近似垂直地穿越分子束约10次。该腔室由一个6英寸的扩散泵、一个爆破泵和一个旋转泵进行评估。吸收信号由锁相放大器处理，由箱车平均器检测，然后在微机中积累。利用该仪器测量了CO分子的红外基波段，发现CO分子在超音速自由膨胀射流中的旋转温度低至3 K，足以产生范德华配合物。测量了（n2o）_2调光剂在1270 cm^<-1>区域对应于单体的nu_1波段（N-O拉伸）的红外吸收光谱，并利用该光谱对分子束的特征进行了详细的研究。新的范德华配合物如OCS-HCI和OCS-N_2O在2200 cm^<-1>的频率范围内被测量到，我们现在正在对它们进行分配。研制了用于检测弱结合配合物的二极管激光微波双共振光谱仪。双共振方法对于配合物的检测具有优点，例如，如果检测到分子配合物的双共振信号，红外光谱的分配就变得明确。我们还对双谐振系统进行了初步测试。少

Detailed studies of weakly bounded molecules are important because the qualitative knowledge about the nature of long range intermolecular forces can be obtained from the spectroscopy of such complexes. The weakly bounded molecules have been studied extensively by Fourier transform microwave spectroscopy combined with pulsed nozzle technique. In addition to rotational spectroscopy in the microwave region, the high resolution infrared studies of the molecular complexes are of great interest because the dynamical properties of the weakly bounded bond such as vibrational predissociation and large amplitude motion can be known directly.In the present study, we developed mid-infrared diode laser spectroscopy for the detection of weakly bounded molecular complexes, such as van der Waals complexes and hydrogen bonded complexes. The weakly bounded complexes were generated in the supersonic free expansion jet using pulsed-nozzle technique, and the infrared absorption spectrum of the complexes w … More ere observed directly. Tunable infrared radiation from a diode laser source was collimated and passed into a high vacuum molecular beam chamber.The laser light traversed the molecular beam approximately perpendicularly to the beam about ten times by means of two near-parallel mirrors. The chamber was evaluated by a 6-inch diffusion pump backed up by a buster pump and a rotary pump. The absorption signal was processed by a lock-in amplifier and detected by a boxcar averager and then accumulated in a micro-computer.Using the present instrument, the fundamental infrared band of CO molecule was measured and the rotational temperature of CO molecule in the supersonic free expansion jet was found to be low as 3 K, which was low enough to produce van der Waals complexes.The infrared absorption spectrum of (N_2O)_2 dimmer in the 1270 cm^<-1> region, which corresponded to the nu_1 band (N-O stretching) of monomer, was then measured and the characteristic features of the molecular beam was examined in detail with use of the spectrum. New van der Waals complexes such as OCS-HCI and OCS-N_2O were measured in the frequency range of 2200 cm^<-1> and we are now making their assignments.The diode laser microwave double resonance spectrometer for the detection of the weakly bounded complexes was also developed. The double resonance method has advantages for the detection of the complexes, for example, the assignments of the infrared spectrum becomes definite if a double resonance signal of the molecular complexes is detected. We also made the preliminary test of the double resonance system. Less