Crossed molecular beam studies on the reaction dynamics of O(1D)+N2O

Structural characterization of the NO(X2Π)-N2O complex with mid-infrared laser absorption spectroscopy and quantum chemical calculations

Both positive and negative ions of N₃O₂ have been observed in various experiments. The neutral N₃O₂ was predicted to exist either as a weakly bound NO·N₂O complex or a covalent molecule. The rovibrational spectrum of the NO(X²Π)-N₂O complex has been measured for the first time in the 5.3 µm region using distributed quantum cascade lasers to probe the direct absorption in a slit-jet supersonic expansion. The observed spectrum is analyzed with a semi-rigid asymmetric rotor Hamiltonian for a planar open-shell complex, giving a bent geometry with an a-axis-NO angle of about 21.9°. The vibrationally averaged ²A'-²A″ energy separation is determined to be ε = 144.56(95) cm^-1 for the ground state, indicating that the electronic orbital angular momentum is partially quenched upon complexation. Geometry optimizations of the complex restricted to a planar configuration at the RCCSD(T)/aug-cc-pVTZ level of theory show that the ²A″ state is more stable than the ²A' state by about 110 cm^-1 and the N atom of NO points to the central N atom of N₂O at the minimum of the ²A″ state.

Laser initiated reactions in N2O clusters studied by time-sliced ion velocity imaging technique

Laser initiated reactions in N2O clusters were studied by a time-sliced velocity imaging technique. The N2O clusters, (N2O)n, generated by supersonic expansion were irradiated by an ultraviolet laser around 204 nm to convert reactant pairs, O((1)D2)-(N2O)n-1. The NO molecules formed from these reactant pairs were ionized by the same laser pulse and their velocity distribution was determined by the time-sliced velocity imaging technique. At low nozzle pressure, lower than 1.5 atm, the speed distribution in the frame moving with the clusters consists of two components. These components were ascribed to the products appeared in the backward and forward directions in the center-of-mass frame, respectively. The former consists of the vibrational ground state and the latter consists of highly vibrational excited states. At higher nozzle pressure, a single broad speed distribution became dominant for the product NO. The pressure and laser power dependences suggested that this component is attributed to the product formed in the clusters larger than dimer, (N2O)n (n ≥ 3).

O((1)D) + N(2)O reaction: NO vibrational and rotational distributions

The O((1)D) + N(2)O → 2NO(X (2)Π) reaction has been studied in a molecular beam experiment in which O(3) and N(2)O were coexpanded. The precursor O((1)D) was prepared by O(3) photodissociation at 266 nm, and the NO(X (2)Π) molecules born from the reaction as the O((1)D) recoiled out of the beam were detected by 1+1 REMPI over the 220-246 nm probe laser wavelength range. The resulting spectrum was simulated to extract rotational and vibrational distributions of the NO(X (2)Π) molecules. The product rotational distribution is found to be characterized by a constant rotational temperature of ≈4500 K for all observed bands, v = 0-9. An inverted vibrational distribution is observed. A consistent explanation of this and previous experimental results is possible if there are two channels for the reaction, one producing a nearly statistical vibrational distribution for low O((1)D)-N(2)O relative velocity collisions and a second producing the inverted distribution observed here for high relative velocity collisions. The former might correspond to an insertion/complex-formation reaction, while the latter might correspond to a stripping reaction. Velocity relaxation of the O((1)D) is argued to compete strongly with reaction in most bulb studies, so that these studies see predominantly the nearly statistical distribution. In contrast, the beam experiments do not detect the part of the vibrational distribution produced in low relative velocity reactions because the O((1)D) is not relaxed from its initial velocity before it either reacts or leaves the beam.