Spectroscopic studies of NdO+ in support of atmospheric release probes of the ionosphere
Abstract
The Air Force Research Laboratory (AFRL) is interested in using an artificial increase in electron density to control radio and microwave opacity in the thermosphere. One strategy for achieving this condition is to use exothermic metal-based chemiionization reactions of the form M + O -> (MO+) + e as the source of free electrons. Attention has been focused on atmospheric release of Sm and Nd atomic vapors at high altitude (>100 km) by sounding rockets. An unexpectedly low yield of SmO+ led to the conclusion that the Sm+O-> (SmO+) + e reaction is almost thermoneutral. This discovery motivated new studies of the thermochemistry of the Nd+O-> (NdO+) + e reaction. Key parameters for the determination of thermodynamics are the molecular ionization energy and the density of low-lying electronically excited states of the NdO+ ion. The primary goal of this research effort was to measure the ionization energy of NdO and characterize the lower energy states of NdO+ by means of two-color photoionization spectroscopy. The value obtained for the ionization energy, 5.5083(2) eV, was 0.54 eV higher thanprevious estimates. Combined with a new determination of the bond energy for NdO+ (Ghiassee et al. J. Chem. Phys. 150, 144309 (2019)) this leads to the conclusion that the chemi-ionization reaction is exothermic by 1.76(10) eV, and promising for future atmospheric release experiments. The spectroscopic measurements for NdO+ have revealed thirty vibronic levels that arise from eight electronic states. Spectra were observed for these states at the level of rotational structure resolution. The energy level pattern and supporting electronic structure calculations indicated that all of the observed states correlated with the Nd(4f3, 4I)O+ configuration. The structure was consistent with a ligand field theory model where the electronic states of the Nd3+(4f3, 4I) atomic ion define a repeat.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 22, 2019
- Accession Number
- AD1097242
Entities
People
- Michael C Heaven
Organizations
- Emory University