THE $\tilde{A}(0,9,0)^2 \leftarrow \tilde{X}(0,0,0)^3$ AND $\tilde{A}(0,9,0)^4 \leftarrow \tilde{X}(0,0,0)^3$ BANDS OF CH$_2^+$

Author Institution: Department of Chemistry, Department of Astronomy \& Astrophysics,; and the Enrico Fermi Institute, The University of Chicago, Chicago; IL, 60637, USAThe methylene ion, $CH_2^+$, is of special theoretical interest because it is both quasi-linear and exhibits a strong Renner-Teller interaction between its ground and first-excited electronic states. At linearity, the ground state is a $^{2}\Pi_{u}$ state that splits into $\tilde{X}^{2}A_{1}$ and $\tilde{A}^{2}B_{1}$ states as the molecule bends. The $\tilde{A}$ state is linear, while the $\tilde{X}$ state is quasi-linear with a barrier to linearity of only 1089 \wn. Since 2002 we have been studying the spectrum of $\text{CH}_2^+$ with our Ti:sapphire laser spectrometer. This spectrometer couples velocity modulation with heterodyne detection for near shot-noise-limited sensitivity. Since last year's symposium we have assigned the $\tilde{A}(0,9,0)^2 \leftarrow \tilde{X}(0,0,0)^3$ and $\tilde{A}(0,9,0)^4 \leftarrow \tilde{X}(0,0,0)^3$ bands.}$ state is labeled using bent notation and the $\tilde{A}$ state is labeled using linear notation.} These bands are the first high-resolution detection of $K_a=3$ levels for the ground state. In addition, the $\tilde{A}(0,9,0)^2 \leftarrow \tilde{X}(0,0,0)^3$ can be combined with the previously studied $\tilde{A}(0,9,0)^2 \leftarrow \tilde{X}(0,0,0)^1$ band} \textbf{121}, 11527 (2004).} to produce $K_a= 3-1$ combination differences for the ground state. The current analysis of the complete near-infrared spectrum will be discussed