An ab initio study of dissociative electron attachment to NaHCO₃ and NaCO₃, and the role of these reactions in the formation of sudden sodium layers

Abstract

One of the mechanisms that has been proposed to explain the phenomenon of sudden sodium layers (SSLs) in the upper atmosphere is dissociative attachment of electrons to sodium compounds such as NaHCO3 and NaCO3. In this study, abinitio calculations have been used to estimate the reaction enthalpies (ΔH°0(NaX + e− → Na + X−)) for NaHCO3 and NaCO3, which are found to be 72 ± 20 (0.75) and 21 ± 30 (0.22) kJmol−1 (eV), respectively. NaHCO3 is then shown to be relatively stable above the mesopause. This property, together with its rather small threshold for dissociative electron attachment, makes NaHCO3 a possible source of SSLs under certain conditions.

Modeling the microphysics of mesospheric ice particles: Assessment of current capabilities and basic sensitivities

“…It has been shown using quantum mechanical theory (Plane, 2000;Petrie, 2004) that sodium bicarbonate and sodium hydroxide both possess a large dipole moment and are effectively hydrated at temperatures below 140 K. In particular, NaHCO 3 is a very interesting candidate since it is expected to be stable and exist in sufficient concentrations ($10 4 cm À3 ) at altitudes between 80 and 90 km (Rajasekhar and Plane, 1993;Plane et al, 1999). Hence, both of these substances must be considered to be likely involved in the formation of mesospheric ice particles.…”

A modelling investigation of sudden sodium layers

“…The layers of atomic Ca and Fe in the upper atmosphere are both significantly depleted relative to that of Na, compared with their relative abundances in chondritic meteorites [Plane, 1991]. However, these electrons would probably require energies of less than 1 eV, as in the case of reaction 2 [Rajasekhar and Plane, 1993]. One explanation may be that Ca and Fe are less volatile than Na in molten meteoritic material [Fegley and Cameron, 1987], and these metals tend to evaporate as stable silicate molecules, whereas Na tends to ablate as atoms.…”

A study of the reaction between NaHCO3 and H: Apparent closure on the chemistry of mesospheric Na

“…In contrast, NaHCO3 is a very stable closed-shell molecule: quantum calculations indicate that the only route back to Na (apart from daytime photolysis) is by reaction with atomic H [Rajasekhar and Plane, 1993]:…”