Spectroscopic characterization of lanthanide oxides and their cations
Our group studies the electronic structure of lanthanide oxides and their corresponding cations for communication applications. In our atmosphere, specifically the ionosphere, the natural electron density fluctuates, due to fluctuation in solar radiation. As electrons interact with radio waves, this natural electron fluctuation prohibits uniform radio wave propagation, affecting radio wave communications. Currently, the United States Air Force (USAF) would like to artificially increase the electron density, such that the total density would be much greater than the natural fluctuations, allowing uniform radio wave propagation.
One method of artificial electron density increase is to chemi-ionize lanthanide metals. In this process, lanthanide metals M react with atomic oxygen to create their corresponding cationic metal oxides MO+ and excess electrons.
M + O → MO+ + e– + ΔE
The energy release in the chemi-ionization process is equal to the difference of the dissociation energy and ionization energy of MO. It is desirable for ΔE > 0 since ionization of MO without dissociation is desired. Neodymium (Nd) is a great candidate as ΔENd = 1.76 eV. Even though its chemi-ionization is thermodynamically neutral, samarium (Sm) is also considered as a candidate due to its high vapor pressure. Recently, the USAF has conducted experiments where they have launched small amounts of either Nd or Sm into the atmosphere to under go chemi-ionization. During the launches, “space clouds” with two distinct color profiles have been observed as well as a fraction of the predicted electron density. Currently the two different colors in the space cloud are being attributed to molecular and atomic production but it is unclear to whether the molecular cation is being formed. Spectroscopic characterization of both MO and MO+ can assist in determining if the molecular cation is being formed in the space clouds.
In our lab, we spectroscopically characterize SmO and NdO as well as their cations SmO+ and NdO+ through various experimental techniques. The ionization energies of SmO and NdO were determined through resonant-enhanced multiphoton ionization (REMPI) and pulsed ionization efficiency (PIE) spectroscopic methods. Currently, low- and high-resolution laser-induced fluorescence (LIF) as well as 1D and 2D dispersed laser induced fluorescence (DLIF) methods are being employed to spectroscopically characterize SmO and NdO. We are employing a one photon-ionization process in efforts to create SmO+ and once production is confirmed, LIF and DLIF will be used to characterize SmO+ . Future work includes characterization of SmO+ as well as NdO+.