Ar-D_(2)O复合物在D_(2)O弯曲振动模附近的新振转子带

New rovibrational subbands of Ar-D_(2)O complex in the D_(2)O bending mode region

稀有气体原子和水分子组成的范德瓦耳斯复合物是研究水和其他原子分子之间相互作用的典型模型.本文利用中红外连续外腔量子级联激光器结合脉冲超声分子束吸收光谱技术,在D_(2)O弯曲振动带(v_(2)=1←0)附近测量了Ar-D_(2)O复合物4个新的振动转动子带.基于赝双原子分子有效哈密顿量,本文对测量到的振动转动谱线和前人报道的下能级所涉及的纯转动谱线进行了最小二乘法全局拟合,得到了包括振动子能级能量、转动常数和离心畸变常数等在内的精确的基态和激发态分子参数.Ar-D_(2)O的D_(2)O弯曲振动激发的振动带头被精确确定为1177.92144(32)cm^(-1),该值比D_(2)O单体的带头红移了约0.458 cm^(-1).将从实验得到的振动子能级能量与基于四维势能面的理论计算结果进行了比较,检验了理论计算方法的精度.

The intermolecular interactions involving the water molecule play important roles in many fields of physics,chemistry,and biology.High-resolution spectroscopy of Van der Waals complexes formed by a rare gas atom and a water molecule can provide a wealth of information about these intermolecular interactions.The precise experimental data can be used to test the accuracies and efficiencies of various theoretical methods of constructing the intermolecular potential energy surfaces and calculating the bound states.In this work,the high-resolution infrared absorption spectrum of the Ar-D_(2)O complex in the v_(2)bending region of D_(2)O is measured by using an external cavity quantum cascade laser.A segmented rapid-scan data acquisition method is employed.The Ar-D_(2)O complex is generated in a slit supersonic jet expansion by passing Ar gas through a vessel containing liquid D_(2)O.Four new rovibrational subbands are assigned in the spectral range of 1150-1190 cm-1,namely ∑(0_(00,v2)=1)←∑(1_(11)),∑(0_(00,v2)=1)←∏(1_(11)),∑(1_(01,v2)=1)∏(1_(10))and∑(1_(01,v2)=1)←∏(l01).The first two subbands belong to the otho-species of Ar-D_(2)O,while the latter two belong to the para-species.The observed ro vibrational transitions together with the previously reported pure rotational spectra having the common lower vibrational sub-states are analyzed by a weighted least-squares fitting using a pseudo-diatomic effective Hamiltonian.An experimental error of 10 kHz for the far-infrared transitions and 0.001 cm^(-1) for the infrared transitions are set in the global fitting when using Pickett’s program SPFIT,respectively.The molecular constants including vibrational substate energy,rotational and centrifugal distortion constants,and Coriolis coupling constant,are determined accurately.The previous results for the ∏(1_(11,v2)=0)substate are found to be likely incorrect.The energy of the ∑(0_(00,v2)=1)and ∑(1_(01,v2)=1)substates are determined experimentally for the first time.The band origin of Ar-D_(2)O in the D_(2)O v_(2)bending mode region is determined to be 1177.92144(13)cm^(-1),which is a red shift about 0.458 cm^(-1)compared with the head of D_(2)O monomer.The experimental vibrational substate energy is compared with its theoretical value based on a four-dimensional intermolecular potential energy surface which includes the normal coordinate of the D_(2)O v_(2)bending mode.The experimental and theoretical results are in good agreement with each other.But the calculated energy levels are generally higher than the experimental values,so,there is still much room for improving the theoretical calculations.