# E $\otimes$ \lowercase{e} VIBRONIC COUPLING IN QUARTET STATES OF R\lowercase{b}$_3$ AND K$_3$ ON HELIUM DROPLETS

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 Title: E $\otimes$ \lowercase{e} VIBRONIC COUPLING IN QUARTET STATES OF R\lowercase{b}$_3$ AND K$_3$ ON HELIUM DROPLETS Creators: Aubock, Gerald; Nagl, Johann; Callegari, Carlo; Ernst, Wolfgang E. Issue Date: 2008 Publisher: Ohio State University Abstract: We present laser-induced-fluorescence (LIF) and magnetic-circular-dichroism (MCD) spectra of the $(2)\,^4\!E^{\prime}\leftarrow (1)\,^4\!A^{\prime}_{2}$ band of \chem{Rb_{3}} and \chem{K_{3}} on He nanodroplets. For \chem{Rb_{3}} we find a progression of four bands, split by spin-orbit (SO) and weakly perturbed by linear vibronic Jahn-Teller (JT) coupling. For \chem{K_{3}} the transition had been previously observed, and interpreted in terms of a linear and quadratic Jahn-Teller coupling in the $(2)\,^4\!E^{\prime}$ state.}\ \textbf{115,} 10265 (2001).} An unambiguous assignment of spectra on He droplets is however difficult due to matrix broadening; MCD spectra are a valuable method to offset this unwanted effect. For \chem{K_3} they clearly reveal the importance of SO coupling and suggest a different assignment with weak linear, and no significant quadratic, JT coupling. Further, interpretation of our data in terms of free-molecule SO indicate that the trimers lie flat on the droplet surface. The observed strong $\mathcal{C}$-type MCD spectra arise from different populations of the ground-state Zeeman sublevels; a quantitative analysis allows a determination of the spin temperature, hence of the temperature at the droplet surface. Our simulations are consistent with a value of 0.4~K, which agrees with our previous findings from spectra of triplet-state alkali-metal dimers.} \textbf{111,} 7404 (2007).} This is the first observation of SO coupling in quartet states of trimers. Description: J. H. Reho, J. Higgins, M. Nooijen, K. K. Lehmann, and G. Scoles, J. Chem. Phys.G. Aubock, J. Nagl, C. Callegari, and W. E. Ernst, J. Phys. Chem. A Author Institution: Institute of Experimental Physics, TU Graz, Petersgasse 16; 8010 Graz, Austria/EU URI: http://hdl.handle.net/1811/33248 Other Identifiers: 2008-WH-12