Knowledge Bank

Weakly bound complexes of the form $Ca+$ -RG (RG = Ar, Kr, Xe) are prepared in a pulsed nozzle/laser vaporization cluster source and studied with mass-selected resonance enhanced photodissociation spectroscopy. The $Ca+$ ($\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}P\leftarrow 2S$) atomic resonance line is the chromophore giving rise to the molecular spectra in these complexes. Vibrationally resolved spectra are measured for these complexes in the corresponding $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi \leftarrow X2\Sigma +$ molecular electronic transition. These spectra are red-shifted from the atomic resonance line, indicating that each complex is more strongly bound in its excited $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi$ state than it is in the ground state. Vibronic progressions allow determination of the excited state vibrational constants: $Ca+$ -Ar, $\omega e\prime =165$ $cm-1$; $Ca+$ -Kr, $\omega e=149$ $cm-1$; $Ca+$ -Xe, $\omega e=142$ $cm-1$. Extrapolation of the excited state vibrational progressions, and combination with the known atomic asymptotes and spectral shifts, leads to determination of the ground state dissociation energies; $Ca+$ -Ar, $D0\prime \prime =700\pm 100$ $cm-1$ (0.09eV); $Ca+$ -Kr, $D0\prime \prime =1400\pm 150$ $cm-1$ (0.17eV); $Ca+$ -Xe, $D0\prime \prime =2300\pm 150$ $cm-1$ (0.29 eV). The spin-orbit splitting in the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi 1/2,3/2$ state for these complexes is larger than expected by comparison to the $Ca+$ atomic value.