A combined experimental and computational study on the transition of the calcium isopropoxide radical as a candidate for direct laser cooling.

Vibronically resolved laser-induced fluorescence/dispersed fluorescence (LIF/DF) and cavity ring-down (CRD) spectra of the electronic transition of the calcium isopropoxide [CaOCH(CH)] radical have been obtained under jet-cooled conditions. An essentially constant energy separation of 68 cm has been observed for the vibrational ground levels and all fundamental vibrational levels accessed in the LIF measurement. To simulate the experimental spectra and assign the recorded vibronic bands, Franck-Condon (FC) factors and vibrational branching ratios (VBRs) are predicted from vibrational modes and their frequencies calculated using the complete-active-space self-consistent field (CASSCF) and equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) methods.

Electronic spectroscopy of the ÃA/ÃA-X̃A transitions of jet-cooled calcium ethoxide radicals: Vibronic structure of alkaline earth monoalkoxide radicals of C symmetry.

Laser-induced fluorescence/dispersed fluorescence (LIF/DF) and cavity ring-down spectra of the ÃA/ÃA-X̃A electronic transition of the calcium ethoxide (CaOCH) radical have been obtained under jet-cooled conditions. An essentially constant Ã-Ã energy separation for different vibronic levels is observed in the LIF spectrum, which is attributed to both the spin-orbit (SO) interaction and non-relativistic effects. Electronic transition energies, vibrational frequencies, and spin-vibrational eigenfunctions calculated using the coupled-cluster method, along with results from previous complete active space self-consistent field calculations, have been used to predict the vibronic energy level structure and simulate the recorded LIF/DF spectra.

Aligning an optical cavity: with reference to cavity ring-down spectroscopy.

A procedure for timely, accurate, and reproducible alignment of an optical cavity is described.

Laser-induced fluorescence and dispersed-fluorescence spectroscopy of the ÃE-X̃A transition of jet-cooled calcium methoxide (CaOCH) radicals.

Laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra of the ÃE-X̃A electronic transition of the calcium methoxide (CaOCH) radical have been obtained under jet-cooled conditions. Complete active space self-consistent field and coupled-cluster calculations on the free radical were performed to aid the assignment of vibronic transitions observed in the LIF/DF spectra. In addition to dominant spectral features that are well reproduced by vibrational frequencies and Franck-Condon (FC) factors calculated ab initio, the FC matrix for the ÃE-X̃A electronic transition contains considerable off-diagonal elements that connect (i) the CaO-stretch (ν) mode and non-CaO stretch modes and (ii) the asymmetric CaOC stretch (ν) and the CaOC bending (ν) modes.

Laser-Induced Fluorescence and Dispersed Fluorescence Spectroscopy of Jet-Cooled Isopentoxy Radicals.

The B̃-X̃ laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra of jet-cooled isopentoxy radicals have been obtained. The LIF spectrum of isopentoxy lacks strong transitions to the CO-stretch levels that are typical for alkoxy radicals. Instead, it contains two low-frequency vibrational progressions due to large-amplitude motions of the GG' and GG conformers involving torsion of the CCCH dihedral angle.

Direct Observation of Tetrahydrofuranyl and Tetrahydropyranyl Peroxy Radicals via Cavity Ring-Down Spectroscopy.

Room-temperature cavity ring-down (CRD) spectra of the à ← X̃ electronic transition of tetrahydrofuranyl peroxy (THFOO) and tetrahydropyranyl peroxy (THPOO) radicals were recorded. The peroxy radicals were produced by Cl-initiated oxidation of tetrahydrofuran and tetrahydropyran. Quantum chemical calculations of the lowest-energy conformers of all regioisomers of these two peroxy radicals have been carried out to aid the spectral simulation.

Dispersed Fluorescence Spectroscopy of Jet-Cooled Isobutoxy and 2-Methyl-1-butoxy Radicals.

We report dispersed fluorescence (DF) spectra of the isobutoxy and 2-methyl-1-butoxy radicals produced by photolysis of corresponding nitrites in supersonic jet expansion. Different vibrational structures have been observed in the DF spectra when different vibronic bands in the laser-induced fluorescence (LIF) spectra of each radical were pumped, which suggests that those vibronic bands be assigned to different conformers. Spectra simulated using calculated vibrational frequencies and Franck-Condon factors well reproduce the experimentally observed ones and support the assignment of the vibronic bands in the LIF spectra to the two lowest-energy conformers of each radical.