Fumie X. Sunahori

The electronic spectrum of the fluoroborane free radical. I. Theoretical calculation of the vibronic energy levels of the ground and first excited electronic states.

The fluoroborane (HBF) free radical has a large vibronic interaction which splits the orbitally degenerate (2)Pi state in the linear configuration into two separate electronic states, one strongly bent and one linear. The observed vibrational structure of the electronic transition between the Renner-Teller pair of states is very complex. As an aid to understanding the spectrum, the vibronic energy levels of the ground and first excited states have been calculated from high-level ab initio potential energy surfaces using a variational method. The vibrational frequencies and anharmonicities have been derived from these energy levels and the boron and hydrogen isotope shifts have been predicted. Although the ground state energy levels are for the most part well behaved, the excited state levels show substantial Renner-Teller mixing with nearby ground vibrational states. The calculations in the present work have been successfully used in the companion paper to make vibrational assignments of the laser-induced fluorescence spectra of HBF and DBF.

The electronic spectrum of the C2P free radical and a Renner–Teller analysis of the Δ2 and X̃Π2 electronic states

Subsequent to our spectroscopic detection of the C(2)X(X=P,As) free radicals [F. X. Sunahori et al., J. Am. Chem. Soc. 129, 9600 (2007)], we have studied the electronic spectrum of the (2)Delta(i)-X (2)Pi(r) system of the jet-cooled C(2)P free radical in the 490-630 nm region. The high-resolution laser-induced fluorescence spectrum of the two spin components of the 0(0) (0) band of (12)C(2)P has been recorded, and the rotational and spin-orbit coupling constants have been determined for both electronic states. The Renner-Teller effect has been observed in both the (2)Pi and the (2)Delta states, and the vibrational structure has been assigned. For the ground state, all of the observed levels up to 3500 cm(-1) were fitted with a standard Renner-Teller model. The excited (2)Delta state vibrational levels were successfully fitted using literature energy level expressions derived from perturbation theory, yielding vibrational and Renner-Teller parameters for both (12)C(2)P and (13)C(2)P. The molecular structure of C(2)P in the ground and excited states has also been estimated and compared to ab initio calculations and the geometries of similar molecules.

Fourier transform microwave spectroscopy of monobromogermylene (HGeBr and DGeBr), a heavy atom carbene analog

Eight isotopologues of HGeBr and nine of DGeBr have been studied in natural abundance by pulsed-jet Fourier transform microwave spectroscopy. The reactive germylene species were produced in an electric discharge at the exit of a pulsed molecular beam valve using precursor mixtures of H(3)GeBr or D(3)GeBr in high pressure neon. In the 5-25 GHz operating range of the spectrometer, only a-type transitions were observed; K = 0 transitions for HGeBr and K = 0 and 1 transitions for DGeBr. From the observed transitions, an improved molecular geometry has been determined and nuclear quadruple constants for Ge and Br have been determined. The Townes-Dailey model has been extended to obtain the electron densities of the 4p orbitals on the germanium and bromine atoms from the quadruple coupling constants. These results are discussed in terms of qualitative molecular orbital theory.

High-resolution infrared spectrum of jet-cooled methyl acetate in the C=O stretching region: Internal rotations of two inequivalent methyl tops

The jet-cooled high resolution infrared (IR) spectrum of methyl acetate (MA), CH(3)-C(=O)-O-CH(3), in the C=O fundamental band region was recorded by using a rapid scan IR laser spectrometer equipped with an astigmatic multipass cell. No high resolution IR analyses of the ro-vibrational transitions between the ground and non-torsionally excited vibrational states have hitherto been reported for molecules with two inequivalent methyl rotors. Because of the two chemically different methyl tops in MA, i.e., the acetyl -CH(3) and methoxy -CH(3), each rotational energy level is split into more than two torsional sublevels by internal rotations of these methyl groups. We were able to assign ro-vibrational transitions of four torsional species by using the ground state combination differences calculated from the molecular constants of the vibrational ground state recently determined by a global fit of the microwave and millimeter wave lines [M. Tudorie, I. Kleiner, J. T. Hougen, S. Melandri, L. W. Sutikdja, and W. Stahl, J. Mol. Spectrosc. 269, 211 (2011)]. The assigned lines were successfully fitted using the BELGI-Cs-IR program to an overall standard deviation which is comparable to the measurement accuracy. This study is also of interest in understanding the role of methyl rotors in the intramolecular vibrational-energy redistribution processes in mid-size organic molecules.