含振动激发卤化氢分子的气体中量子态分辨能量转移过程实验研究

Highly vibrationally excited hydrogen halides are prepared using degenerate stimulated hyper-Raman pumping. The probe laser is used to excit A1Σ+(v′,J′) states of hydrogen halides. The time-resolved laser induced fluorescence intensity decay curves of A1Σ+-X1Σ+ states are prepared. The data demonstrate that single rate coefficient measurements are unlikely to capture the complex nature of processes that generally are multistaged with different relaxation rate characterising each different stage. The collisional relaxation rate coefficients of highly vibrationally excited states are continuous variation in the same stage. The population distributions of various vibrational levels through collisional relaxation are determined by measuring time-resolved fluorescence intensity. The time evolutions and relaxative populations of the vibrational states (≤v) after preparation of v state are measured. Each vibrational state relative population is obtained at the same time delay tD. The vibrational population is characterized by a Boltamann vibrational temperature (Tvib) for different time delay. The instantaneous LIF intensity of each rotational level on the hydrogen halide molecule vibrational level is recorded. The time evolutions and relative populations of the rotational states (<J) after preparation of (v, J) state also are measured. The rotational populations are characterized by a Boltamann rotational temperature (Trot). The translational temperatures (Ttran) are obtained by measuring the Doppler broadened transient line shapes for the absorption transition Χ1Σ+(v,J)-A1Σ+(v′,J′). When the fast multiquantum vibrational relaxation of highly vibrationally excited hydrogen halides permit maximum amounts of energy are deposited into partner species by V-V or V-R exchange, the vibrational temperature (Tvib) of excited hydrogen halides falls rapidly. The rotational transient population distribution of the acceptor molecules from V-RT energy transfer are measured by multipass overtone absorption. Fitting the experimental data yields state-specific rate constants of depletion and appearance, respectively. Correlation between the average change in angular momentum and the average change of recoil velocity from V-RT collisions is determined. The energy transfer probability distribution function is presented.

本项目利用简并受激超拉曼泵浦激发卤化氢分子的高位振动态Χ1Σ+(v,J)，再由检测激光将其激发到A1Σ+(v′,J′)态。通过测量时间分辨激光诱导荧光(LIF)强度衰减曲线可得高振动态分子碰撞弛豫速率系数分阶段变化情况。测量由碰撞弛豫得到布居的卤化氢分子各振动能级时间分辨LIF光强可得该能级布居分布，由相同延迟时间下各振动能级相对布居，得到振动温度Tvib。改变延迟时间，得到Tvib的时间演化曲线。测量卤化氢分子振动能级上各转动能级的瞬时LIF光强，得到转动温度Trot。测量Χ1Σ+(v,J)-A1Σ+(v′,J′)吸收线的瞬时多普勒增宽，得到平动温度Ttran。在振动-转动平移（V-RT）能量转移中，利用多光程泛频吸收测量受主分子转动态瞬时布居，拟合实验数据可得布居的倒空和出现速率系数。确定V-RT转移中平均速度的增加和角动量改变的关系，给出碰撞中的能量转移概率分布函数。

激发态分子的振动-振动（转动）碰撞弛豫过程在天体物理、大气化学、冷和超冷分子等领域中起到重要作用，是气相分子动力学的研究热点之一。项目组利用简并受激超拉曼泵浦激发HBr (DBr)分子，研究了激发态分子与其他气体分子的碰撞弛豫过程。. 激发HBr(Χ1Σ+ v′′=5)振动态，测量与N2, CO2, H2和HBr碰撞后v′′≤5各振动态瞬时LIF时间演化，得到碰撞弛豫速率系数分别为0.05, 5.3, 0.4和2.1×10-12 cm3molecule-1s-1。N2的0-1转移速率系数比CO2的(0000)-(0001)转移速率系数小2个量级，是HBr自弛豫的0-1振动转移速率系数的1/40。碰撞分子的振动跃迁红外活性越强，能量转移速率系数越大。激发DBr(v′′=7,8)，讨论其与D2，Ar的碰撞弛豫过程。对HBr-H2和DBr-D2的碰撞，观察到了二量子弛豫的直接证据；对HBr-N2（CO2）和DBr-Ar的碰撞，只有连续单量子振动弛豫。结果表明，振动-振动近共振能量转移是高振动激发态分子弛豫的一个重要机制。. 激发DBr（8,8）态，由瞬时双光子吸收方法确定有效线强度修正因子，得到各转动能级的相对布居数。在一次碰撞条件下，得到ΔJ′≤3时DBr（8, J′≠8）各转动态的转移速率系数范围为1.9×10-11-5.1×10-10cm3molecule-1s-1；DBr（8,7）的猝灭率为3.6×107s-1。在多次碰撞环境中，测量了激发态DBr分子的平动、转动和振动模温度随延迟时间的演化。数据表明，振动弛豫是一个分阶段变化的复杂过程，不能用单一速率系数表征。而平动和转动温度在碰撞过程中不断变化，保证系统能够迅速达到平衡。. 激发HBr（1, J′=12,14）激发态，在一次碰撞条件下，测量HBr(E)/CO2碰撞前后CO2(0000,J)态泛频激光感应荧光强度比，得到CO2转动态的双指数分布，拟合实验数据得到弱碰撞的低温分布占被散射布居的65%（60%），强碰撞的高温分布占35%（40%）。碰撞后CO2转动态的总出现速率系数为1.3（2.7）×10-10cm3molecule-1s-1，低转动态的平均倒空速率系数为2.9（2.8）×10-10cm3molecule-1s-1。总出现速率系数与平均倒空速率系数在量级上保持一致.

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