Dynamical Resonances in Chemical Reactions and Chemical Bonding

Valentini博士获得了物理化学计划的资助，研究气相化学反应中过渡态的结构和动力学。瓦伦蒂尼开发了一种光谱技术，可以间接观察短寿命的中间产物（过渡态），这些中间产物长期以来一直在理论上被预测，但从未在化学反应中被观察到。瓦伦蒂尼博士的研究涉及所谓的费什巴赫共振在旋转激发横截面的研究，这是在气相化学反应中观察到的。直接观察涉及状态到状态的动力学，其中反应物的振动和旋转量子态（v,j）是通过自由射流膨胀冷却制备的，并通过受激拉曼激发探测。通过激光光解双原子前驱体生成反应物原子，选择、改变和精确指定反应物的碰撞能量。利用共振增强的多光子电离对单碰撞条件下反应产物的振动和旋转（v′，j′）进行了分析。瓦伦蒂尼博士的研究计划的动机是他最近发现的费施巴赫共振在正、对氢交换反应。这个观察使他能够推断出在这个反应中发生的线性三原子过渡态的振动能态。该领域的进一步研究将涉及氢氘交换反应，氯与氯化氢的反应，碘和溴与相应的卤化氢的反应。将获得这些物质的相干拉曼光谱，以阐明理论预测的振动键的性质。

Dr. Valentini is supported by a grant fom The Physical Chemistry Program to study the structure and dynamics of transition states in gas phase chemical reactions. Valentini has developed a spectroscopic technique which permits the indirect observation of the short-lived intermediates (transition states) which have long been theoretically predicted but never observed in chemical reactions. Dr. Valentini's research involves the studies of so-called Feshbach resonances in rotational excitation cross sections which are observed for chemical reactions in the gas phase. The direct observations involve state-to-state dynamics in which the vibrational and rotational quantum states (v,j) of the reactants are prepared by free-jet expansion cooling and probed by stimulated Raman excitation. The collision energy of the reactants is selected, varied, and precisely specified through laser photolysis of a diatomic precursor to generate the reactant atom. Vibrational and rotational (v',j') analysis of the reaction products under single collision conditions are effected using resonance-enhanced multiphoton ionizaiton. Dr. Valentini's research program is motivated by his recent discovery of Feschbach resonances in the ortho-, para-hydrogen exchange reaction. This observation permitted him to infer the vibrational energy states of the linear triatomic transition state which occurs in this reaction. Further studies in this area will involve the hydrogen deuterium exchange reaction, the reaction of chlorine with hydrogen chloride, and the reaction of iodine and bromine with their corresponding hydrogen halides. Coherent Raman spectra of these species will be obtained to elucidate the nature of the theoretically predicted vibrational bonding.