Dipartimento di Chimica Fisica, Università Ca' Foscari Venezia, Calle Larga Santa Marta 2137, I-30123 Venezia, Italy.
J Chem Phys. 2010 Jan 28;132(4):044316. doi: 10.1063/1.3299263.
Information about intermolecular potentials is usually obtained through the analysis of the absorption line shapes recorded in the frequency domain. This approach is also adopted to study the effects of motional narrowing and speed dependence of the pressure broadening coefficients. On the other hand, time domain measurements are directly related to molecular collisions and are therefore frequently employed to study molecular relaxation rates, as well as the effects of velocity changing collisions and the speed dependence of the absorption cross sections. Intrapulse quantum cascade laser spectrometers are able to produce both saturation and molecular alignment of the gas sample. This is due to the rapid sweep of the radiation through the absorption features. In the present work the frequency down-chirped radiation emitted by an intrapulsed quantum cascade laser operating near 7.8 mum is employed to investigate the collisional relaxation processes, and the collisional narrowing, in the 15(0,15)<--16(1,16) and 15(1,15)<--16(0,16) doublet in the water vapor nu(2) band. The effects of He, Ne, Ar, N(2), and CO(2) as collisional partners are investigated. The experimental results clearly indicate the dependence of the collisional cross sections upon the chirp rate. They also demonstrate that by using different chirp rates it is possible to gain information about the intermolecular processes driving the molecular collisions and the related energy transfer.
分子间势能的信息通常通过分析在频域中记录的吸收线形状来获得。这种方法也被用于研究运动变窄和压力展宽系数的速度依赖性的影响。另一方面，时域测量直接与分子碰撞有关，因此常用于研究分子弛豫率，以及速度变化碰撞的影响和吸收截面的速度依赖性。脉冲内量子级联激光光谱仪能够产生气体样品的饱和和分子取向。这是由于辐射通过吸收特征的快速扫描。在本工作中，利用在接近 7.8 µm 处工作的脉冲内量子级联激光发射的频率下啁啾辐射，研究了水蒸气 ν2 带中 15(0,15)<--16(1,16)和 15(1,15)<--16(0,16)双原子的碰撞弛豫过程和碰撞展宽。研究了 He、Ne、Ar、N2 和 CO2 作为碰撞伙伴的影响。实验结果清楚地表明了碰撞截面对啁啾率的依赖性。它们还表明，通过使用不同的啁啾率，可以获得有关驱动分子碰撞的分子间过程和相关能量转移的信息。
