The ground state of KO revisited: the millimeter and submillimeter spectrum of potassium oxide.

The millimeter/sub-millimeter spectrum of the KO radical has been recorded in the frequency range 90-534 GHz using direct absorption methods. The radical was synthesized by reacting potassium vapor, produced with a Broida-type oven, with either N2O or O2 mixed in argon carrier gas. Twenty-seven rotational transitions of KO were measured, each exhibiting a doublet structure with a relatively small splitting (∼100-200 MHz) that increased noticeably with frequency. A perturbation was apparent in the rotational lines at energies above ∼120 cm-1, which was more prominent in one doublet component. The data were successfully fit with a Hund's case (c) Hamiltonian, assuming that spectra arise from a 2Πi state, and rotational and effective lambda-doubling constants were determined. Higher order centrifugal distortion terms were needed to account for the perturbation. The spectra could also be fit as a 2Σ+ ground state, but less successfully, and the resulting rotational constant of B = 8235.4 MHz disagreed significantly with that predicted by theory. On the basis of the experimental data, the ground electronic state of KO has been assigned as 2Πi, although the 2Σ+ assignment cannot be entirely ruled out.

Applied quantum chemistry: Spectroscopic detection and characterization of the F2BS and Cl2BS free radicals in the gas phase.

In this and previous work [D. J. Clouthier, J. Chem. Phys. 141, 244309 (2014)], the spectroscopic signatures of the X2BY (X = H, halogen, Y = O, S) free radicals have been predicted using high level ab initio theory. The theoretical results have been used to calculate the electronic absorption and single vibronic level (SVL) emission spectra of the radicals under typical jet-cooled conditions. Using these diagnostic predictions, the previously unknown F2BS and Cl2BS free radicals have been identified and characterized. The radicals were prepared in a free jet expansion by subjecting precursor mixtures of BF3 or BCl3 and CS2 vapor to an electric discharge at the exit of a pulsed molecular beam valve. The B̃(2)A1-X̃(2)B2 laser-induced fluorescence spectra were found within 150 cm(-1) of their theoretically predicted positions with vibronic structure consistent with our Franck-Condon simulations. The B̃(2)A1 state emits down to the ground state and to the low-lying Ã(2)B1 excited state and the correspondence between the observed and theoretically derived SVL emission Franck-Condon profiles was used to positively identify the radicals and make assignments. Excited state Coriolis coupling effects complicate the emission spectra of both radicals. In addition, a forbidden component of the electronically allowed B̃-X̃ band system of Cl2BS is evident, as signaled by the activity in the b2 modes in the spectrum. Symmetry arguments indicate that this component gains intensity due to a vibronic interaction of the B̃(2)A1 state with a nearby electronic state of (2)B2 symmetry.

Structural determination and gas-phase synthesis of monomeric, unsolvated IZnCH3 (X̃(1)A(1)): a model organozinc halide.

The first experimental structure of a monomeric organozinc halide, IZnCH3, has been measured using millimeter-wave direct absorption spectroscopy in the frequency range 256-293 GHz. IZnCH3 is a model compound for organozinc halides, widely used in cross-coupling reactions. The species was produced in the gas phase by reaction of zinc vapor with iodomethane in the presence of a dc discharge. IZnCH3 was identified on the basis of its pure rotational spectrum as well as those of the isotopically substituted species I(66)ZnCH3, I(64)Zn(13)CH3, and I(64)ZnCD3. IZnCH3 is unmistakably a symmetric top molecule (X̃(1)A1) belonging to the C3v point group, in agreement with DFT calculations, with the following experimentally determined structural parameters: rIZn = 2.4076(2) Å, rZnC = 1.9201(2) Å, rCH = 1.105(9) Å, and ∠H-C-H = 108.7(5)°. The basic methyl group geometry is not significantly altered in this molecule. Experimental observations suggest that IZnCH3 is synthesized in the gas phase by direct insertion of activated atomic zinc into the carbon-iodine bond of iodomethane.

An experimental and ab initio study of the electronic spectrum of the jet-cooled F2BO free radical.

We have studied the B̃ (2)A1-X̃ (2)B2 laser-induced fluorescence (LIF) spectrum of the jet-cooled F2BO radical for the first time. The transition consists of a strong 0(0)(0)band at 446.5 nm and eight weak sequence bands to shorter wavelengths. Single vibronic level emission spectra obtained by laser excitation of individual levels of the B̃ state exhibit two electronic transitions: a very weak, sparse B̃-X̃ band system in the 450-500 nm region and a stronger, more extensive set of B̃ (2)A1-à (2)B1 bands in the 580-650 nm region. We have also performed a series of high level ab initio calculations to predict the electronic energies, molecular structures, vibrational frequencies, and rotational and spin-rotation constants in the X̃ (2)B2, à (2)B1 and B̃ (2)A1 electronic states as an aid to the analysis of the experimental data. The theoretical results have been used as input for simulations of the rotationally resolved B̃ (2)A1-X̃ (2)B2 0(0)(0) LIF band and Franck-Condon profiles of the LIF and single vibronic level emission spectra. The agreement between the simulations obtained with purely ab initio parameters and the experimental spectra validates the geometries calculated for the ground and excited states and the conclusion that the radical has C2v symmetry in the X̃, Ã, and B̃ states. The spectra provide considerable new information about the vibrational energy levels of the X̃ and à states, but very little for the B̃ state, due to the very restrictive Franck-Condon factors in the LIF spectra.

Optical-optical double resonance spectroscopy of the C(2)Pi-A(2)Pi and D(2)Sigma(+)-A(2)Pi transitions of SrF.

Optical-optical double resonance spectroscopy has been used to record rotationally resolved spectra of the C(2)Pi-A(2)Pi and D(2)Sigma(+)-A(2)Pi transitions of SrF. In the investigation, the spectrum of a previously unobserved (2)Sigma(+)-A(2)Pi transition was recorded. The new (2)Sigma(+) state was found to lie lower in energy than the previously labeled D(2)Sigma(+) (v = 0) state by an amount equal to the vibrational spacing of the D(2)Sigma(+) state. Therefore, the new (2)Sigma(+) state was assigned as the v = 0 level of the D(2)Sigma(+) state and the previous labeling of the vibrational quantum numbers of the D(2)Sigma(+) state should be increased by 1. Spectroscopic parameters were determined for the C(2)Pi, D(2)Sigma(+) (v = 0), and D(2)Sigma(+) (v = 1) states. The D(2)Sigma(+) (v = 0) state was found to be perturbed, most likely by the spin-orbit components of the C(2)Pi (v =1) state. The spin-orbit constant of the C(2)Pi state was found to decrease significantly relative to the A(2)Pi state, similar to CaF and SrOH. Finally, the C(2)Pi and D(2)Sigma(+) states do not appear to form a unique perturber/pure precession pair of states.