Photodissociation of NH2: Two-dimensional potential energy surfaces for the dissociation into NH and H

Abstract

Extensive multireference configuration interaction calculations were carried out in order to obtain complete two-dimensional (2D) potential energy surfaces for the amidogen (NH2) radical as functions of both N–H bond lengths keeping the bond angle fixed at its experimental ground state equilibrium value. The eight lowest-lying states (four of each symmetry, A′ and A″) were treated mainly for the purpose of using these surfaces in subsequent studies of the photodissociation dynamics. In analogy with the neighboring dihydrides CH2 and H2O the photodissociation of NH2 into NH+H (hydrogen abstraction) takes place preferentially after excitation of the first two Rydberg s states (3 2A′/2 2A1 and 2 2A″/2 2B1) found closely together at about 7.6 eV. The transition dipole moments connecting the ground state with these two states are large (0.44 a.u. and 0.66 a.u.) in the Franck–Condon region, but the behavior of the potentials in the dissociation channel is quite different. The 3 2A′/2 2A1 state is weakly repulsive whereas the 2 2A″/2 2B1 state is strongly repulsive. This will result in differences in the dissociation dynamics for the two states. The next higher state which should play a role in the NH2 photodissociation is the 4 2A″/3 2B1 Rydberg s state at 9.4 eV, because of its large transition dipole moment with the ground state (0.36 a.u.). Close to this state, many Rydberg p states were found. Due to the high density of states in the region above 9.0 eV, interactions of these states are expected and should lead to complicated dissociation dynamics. Contrary to CH2, the two low-lying valence states for NH2 are found at lower energies [2.2 eV (1 2A1) and 6.5 eV (1 2B2)], well separated from the first members of the Rydberg series. These states are less important for the photodissociation of NH2, compared with CH2, because the first state is bound and the transition to the other is dipole-forbidden in C2v symmetry. For H2O, the valence states are missing.

Time-resolved diagnostics and kinetic modelling of the ignition transient of a H2 + 10% N2 square wave modulated hollow cathode discharge

“…The c-a transition was also found in NH 2 photodissociation experiments [43], but in that work the analysis was focused on the formation of NH(A 3 ) and, as far as we know, no additional direct experimental evidence for this process is available in the literature. The energetic threshold for the production of NH (c 1 Π) from the ground state of NH 2 is close to 10 eV [44] and thus similar to that found in NH 3 . Although the high density of NH 2 Rydberg states in the region above 9 eV is expected to lead to a complex dissociation dynamics [44], the details are again not known.…”

“…The energetic threshold for the production of NH (c 1 Π) from the ground state of NH 2 is close to 10 eV [44] and thus similar to that found in NH 3 . Although the high density of NH 2 Rydberg states in the region above 9 eV is expected to lead to a complex dissociation dynamics [44], the details are again not known.…”

Accurate double many‐body expansion potential energy surface by extrapolation to the complete basis set limit and dynamics calculations for ground state of NH2

“… is a well‐established prototype for the study of insertion reactions, with the reaction also playing a key role in the combustion of nitrogen‐containing materials. During the past decade, the reaction has been much studied both experimentally and theoretically . There are five electronic doublet states correlating with the title reaction, and this reaction is a prototype for studying nonadiabatic effect.…”

Photodissociation and photoionisation of atoms and molecules of astrophysical interest

“…Here, a photodissociation cross section file was composed, from data for the very weak 1 2 A → 2 2 A transition between 150 and 210 nm (Saxon et al 1983) added to the shorter-wavelength cross sections due to stronger transitions to various excited states calculated by Koch (1997) based on potential energy surfaces calculated by Vetter et al (1996). An additional 2 nm FWHM Gaussian line of integrated cross section 10 −16 cm 2 nm was added to the photodissociation cross section at 110 nm to account for excitation into states not considered in the two calculations.…”