The Photodissociation Dynamics Of Some Nitro-and Nitroso Compounds

Photodissociation, considered as the second half of a collision, has been an active field in chemical physics. A simple molecular photodissociation picture can be described as that a molecule is excited by a photo-absorption then to form transient intermediate and then suffers an ultrafast evolution to produce the final fragments. In the last few decades it has been demonstrated that the use of lasers and molecular beam in photodissociation studies yields detailed information about the dynamics of such process. Laser-induced fluorescence (LIF) provides a pathway to investigate the photodissociation dynamics, from which one get the internal state distribution of nascent photofragments directly by measuring their fluorescence excited spectra. The photodissociation of nitro- and nitroso-compounds plays an important role in the environment and combustion chemistry, the study of explosive materials dissociation. The following points are mainly concerned:1. The 266 nm photodissociation of gaseous C6H5NO has been studied by monitoring the nascent NO (X2 п v" =0-3) product using a single-photon laser induced fluorescence technique. The rotational state distributions of the nascent NO photofragment have been measured and can be characterized by Boltzmann temperatures. The vibrational state and A -doublet populations were alsodetermined. Energy disposal into the internal degrees of freedom of NO (X2 ) photofragment is about 19% of the total available energy. Some planarity in thefragmentation process was observed. The alignment A(2) between the electronictransition dipole moment involved in the absorption of the parent molecule and the rotational angular momentum J of the photofragment NO (v" =0,1) has been measured.2. Photodissociation of NO2 at B2B2 state has been studied by monitoring the nascent NO X2 product using the single-photon laser-induced fluorescence technique. The rotational distributions of the nascent NO photofragment after photodissociation of NO2 at B2B2 state have been firstly reported. In NO X2 v " =1 fragment, the rotational distributions are bimodal. We proposed that there are two dissociation mechanisms that govern the product internal distributions at NO2 B2B2 state. The dissociation mechanism in the first and second absorption band was compared.3. The 266 nm photodissociation of gaseous nitrobenzene has been studied by monitoring the NO X2 product using the single-photon laser induced fluorescence technique. The rotational population and internal energy distributions of fragment NO product were determined. In the experiment, we only observed the rotational state distributions of NO fragment for v" =0. The rotational state distributions of the nascent NO photofragment can be characterized by Boltzmann temperature of 3300 300 K. Ab initio calculations were performed to characterize the transition state and to determine the barrier height for rearrangement of nitrobenzene to phenylnitrite. A clear photodissociation picture has been proposed theoretically.4. The 266 nm photodissociation of gaseous nitroethane has been studied bymonitoring the NO (X2 ) product using a single-photon laser induced fluorescence technique. The rotational state distributions of the NO (X2 1/2 and X2 3/2, v" =0) photofragment have been measured and can be characterized by Boltzmann temperature of 710 100 K and 780 100 K respectively. It is estimated at least 90% of the NO is produced in v" =0. The geometries of the nitroethane, the ethyl nitrite and the transition state between the two isomeric structures are fully optimized with MO theory at the MP2/6-31G level. The barrier height for rearrangement of nitroethane to ethyl nitrite has been determined to be 63.47 KcaL/mol. The reasonable photodissociation process has been proposed based on the calculations.