Photodissociation cross sections and rates of NaO

Abstract

ABSTRACT Photodissociation of NaO may be important for the sodium chemistry in various astrophysical regions. This work produces the photodissociation cross sections and rates of NaO over the temperature range from 0 to 15 000 K. First, the state-resolved cross sections for transitions from the ground and first excited states of NaO are investigated using ab initio potential energy curves and transition dipole moments. The temperature-dependent cross sections were then obtained by assuming a Boltzmann distribution to describe the population of the initial state. Detailed comparisons with experimental cross sections at 200 and 300 K reveal that the X 2Π → 1 2∆ and X 2Π → 2 2Σ− transitions may be the main photodissociation pathways for NaO in the wavelengths of about 2400–2580 Å, while the X 2Π → B 2Σ− transition may play a dominant role in the wavelengths of about 3534–4230 Å. Finally, photodissociation rates in the interstellar, solar, and blackbody radiation fields were determined. In the interstellar and solar radiation fields, the X 2Π → B 2Σ− transition dominates at low temperatures and the A 2Σ+ → 2 2Σ+ transition dominates at high temperatures. The total photodissociation rates in ultraviolet-rich and visible-rich radiation fields are almost insensitive to the temperature. The photodissociation cross sections and rates of NaO should be useful for investigating the chemical evolution of the sodium element in planetary exospheres, atmospheres of cool stars, and envelopes of evolved stars.