Predissociation Dynamics of B State of Methyl Iodide with Femtosecond Pump-probe Technique

The predissociation dynamics of B Rydberg state of methyl iodide is studied with femtosecond two-color pump-probe time-of-°ight spectra at pump pulse of 400 nm and probe pulse of 800 nm. The dominant product channels are the CH3I+ and CH3+ formation. The time-dependent signals for CH3I+ and CH3+ ions are obtained. Both of the signal curves can be ˉtted by biexponential decays with time constants of ?1 and ?2, ?1 is assigned to the lifetimes of high Rydberg states, which can be accessed by absorbing three 400 nm pump pulses and ?2 re°ects the dynamics of B Rydberg state, which is accessed with two pump pulses. The lifetime of B Rydberg state is determined to be about 1.57 ps, which is incredibly consistent with the previous studies. The results were interpreted as a multiphoton dissociative ionization processes.     

CS2 分子 1 B2(1 Σ+u )态预解离动力学研究

The predissociation dynamics of CS2 at the g vibrational level of the 1B2(1Σu+) state has been studied, by measuring the predissociation lifetimes from the photofragment CS excitation (PHOFEX) spectrum and the ro vibrational populations of CS fragment from the laser induced fluorescence(LIF) spectrum. It is found that the angular momentum quantum number K of the g level accelerates the dissociation speed of CS2 at the 1B2(1Σu+) state, and increases the branching ratio of S(1D2)/S(3PJ) for the two dissociation channels, CS(X 1Σ+)+S(1D2) and CS(X 1Σ+)+S(3PJ). The dissociation mechanism was discussed based upon the observations.     

Interpretation of predissociation in the V′=3 level ofB 3Π0+ state of I35Cl and I37Cl

The observed oscillatory linewidths of theV′=3 level ofB ³Π₀₊ state of I³⁵Cl and I³⁷Cl are explained as due to heterogeneous predissociation caused by the crossing of an unstableZ ¹Π state. The crossing point and the slopes of the curves have been fixed to predict the observed linewidths.     

弯曲振动对CS_2分子~1B_2(~1Σ_u~+)态预解离寿命的影响

在209.5～216nm,采用光解碎片激发(PHOFEX)谱技术,对CS2分子1B2(1Σ+u)态预解离寿命进行了 考察.测量在超声射流中进行.信号来自解离碎片CS(A1Π,v′=0←X1Σ+,v″=0)Q支带头的激光诱导荧光 (LIF).预解离寿命是通过对谱带进行拟合来提取的.拟合中假定基态转动布居为Boltzmann分布,寿命加宽的转 动谱线为Lorentz线形.通过拟合共获得1B2(1Σ+u)态13个跃迁所对应的预解离寿命,其中6个数据是新得到的. 结果表明,基态振动角动量量子数l或激发态转动角量子数K(K=l)对预解离寿命有明显的影响.对于激发态的 同一振动能级,较大的K对应于较短的预解离寿命.实验中采用可加热的射流喷嘴,用以提高热带激发的强度, 以改善对较大转动角量子数K的影响的考察.     

MRCI studies on ground and excited states of CBr

Potential curves and spectroscopic constants for a large number of doublet and quartet states of CBr were obtained by multireference configuration interaction calculations, using valence triple-zeta basis sets with polarization and diffuse functions. Besides the X²Π ground state, 1⁴Σ^?, 1²Δ and 2²Σ⁺ have been found to be stable. Spectroscopic constants calculated for 1²Δ are in excellent agreement with experimental values obtained by Dixon and Kroto in 1963. Their observed predissociation of one component of 1²Δ can be explained by the crossing of the 1²Δ potential near equilibrium by 1²Σ⁺. The 1²Σ⁺ state is calculated to have a shallow long-range minimum at 2.31?Å. The dissociation energy of X²Π is calculated to be 3.43?eV. An observed T _e of 4.97?eV for 2²Σ⁺ agrees with the theoretical value. Several Rydberg states of the 2π→Ryd and 3σ→Ryd series, starting at T _e ?=?5.25?eV, were identified. Photodissociation of CBr by sunlight, important in the ozone cycle, can occur via direct dissociation of the ground state, or by excitation to 1²Δ followed by predissociation. Most dissocative repulsive states lie at higher energies, and are not expected to participate in the photodisscociation of CBr.     

CuH分子A1∑+态的寿命和预解离研究

A combined cavity ringdown (CRD) and laser induced fluorescence (LIF) spectroscopic study on the A¹∑⁺-X¹∑⁺ transition of CuH has been presented.The CuH molecule,as well as its deuterated isotopologue CuD,are produced in a supersonic jet expansion by discharging H₂(or D₂) and Ar gas mixtures using two copper needles.Different profiles of relative line intensities are observed between the measured LIF and CRD spectra,providing an experimental evidence for the predissociation behavior in the A¹∑⁺ state of CuH.The lifetimes of individual upper rotational levels are measured by LIF,in which the J''-dependent predissociation rates are obtained.Based on the previous theoretical calculations,a predissociation mechanism is concluded due to the strong spin-orbit coupling between the A¹∑⁺ state and the lowest-lying triplet ³∑⁺ state,and a tunneling effect may also be involved in the predissociation.Similar experiments are also performed for CuD,showing that the A¹∑⁺ state of CuD does not undergo a predissociation process.     

Theory of Vibrational Predissociation Spectroscopy

A theory of vibrational predissociation spectroscopy is developed based on the adiabatic approximation that separates the oscillations of the high frequency vibron and low frequency phonon. We find that some properties such as dissociation energy and the number of phonon modes have significant influence on the temperature dependent spectra. Thus a comparison between the present theory and experiment would be a useful approach in determining these properties.     

低振动激发HeI2分子振动预离解寿命和终转动态分布

用含时黄金规则波包法，对ＨｅＩ２分子在低初始振动激发（ｖ＜１２）态下振动预离解动力学作了全维量子力学计算。所预言的总衰变宽度和寿命与谱线宽和皮秒时间分解的实时态－态测量外推数据符合得相当好。计算的总衰变宽度对初始振动态ｖ是敏感的并呈现一种非线性关系。结果表明低振动激发ＨｅＩ２分子衰变模式仍应是量子力学的。除终态相互作用对决定终转动分布有重要作用以外，首次发现，低振动激发态的初始特性也能显著影响终转动态分布。用Ｉ２的转动常数对ｖ的关系合理地解释了这个独特现象     

乙烯自由基A2A''(v'=0)←X2A'(v''=0)带的转动分析

通过193 nm光解丁烯酮分子产生乙烯基自由基(C₂H₃). 经射流冷却后, 用另一束激光光解C₂H₃, 生成的氢原子碎片经共振增强多光子电离(REMPI)过程, 记录氢离子信号随光解波长变化, 得到20020～20070 cm_-1范围内乙烯基激发的转动分辨光谱. 该谱对应于A²A'(v'=0)←X²A'(v'=0)跃迁的转动结构. 结合量子化学理论计算、光谱拟合以及前人的研究结果, 对该段光谱进行了完整的转动识别, 确定了40条转动谱线的位置. 由光谱拟合还得到A²A'(v'= 0 )能级的预解离寿命为3.3 ps, 且不依赖于转动量子数.     

Nonadiabatic quantum dynamics of Br2 in solid Ar: A four-dimensional study of the B to C state predissociation

Quantum dynamics simulations are performed for a diatomics-in-molecules based model of Br₂ in solid Ar which incorporates four nuclear degrees of freedom and four electronic states. The nuclear motions comprise two large amplitude coordinates describing the Br₂ bond distance and an effective symmetry-preserving matrix mode. Two symmetry-lowering harmonic modes are added in the spirit of linear vibronic coupling theory. Initiating the dynamics on the B state by means of an ultrafast laser pulse, nonadiabatic transitions to the two degenerate C states are monitored and the effect of vibrational preexcitation in the electronic ground state is investigated.