Christopher C. Carter

The structure of floppy molecules: the Rg·XH/D (Rg=Ar, Ne, and Kr, X=O or S) family of complexes

Abstract The “structure” of Rg·XH/D weakly bound complexes, where Rg=Ne, Ar and Kr and X=O or S is reviewed. These species likely constitute the most thoroughly studied, broad family of complexes. Due to the open shell nature of OH and SH, the bonding in these complexes ranges from quite weak to incipient chemical. Most of the experimental data concerning these species come from the rotational and vibrational structure of the electronic transition, A 2 Σ + – X 2 Π 3/2 . Based on the spectral work, empirical potential surfaces for both the X 2 Π 3/2 and A 2 Σ + states of the complexes have been developed. These potentials can be used to illustrate the structure and bonding of the complexes. They also can be used to elucidate observed dynamical processes in the complexes.

EMPIRICAL POTENTIAL ENERGY SURFACE FOR AR. SH/D AND KR. SH/D

Experimental data from vibrationally and rotationally resolved laser induced fluorescence experiments have been used to produce potential energy surfaces (PES) for the excited A 2Σ+ states of the Ar⋅SH and Kr⋅SH van der Waals complexes. This was done using a potential energy functional form first suggested by Bowman and co-workers [J. Phys. Chem. 94, 2226, 8858 (1990); Chem. Phys. Lett. 189, 487 (1992)] for Ar⋅OH/D. A discrete variable representation (DVR) of the vibration–rotation Hamiltonian was used in combination with the implicitly restarted Lanczos method and sequential diagonalization truncation (SDT) of the DVR Hamiltonian. This approach takes advantage of the sparseness of the DVR Hamiltonian and the reduced order of the SDT representation. This combination of methods greatly reduces the amount of computational time needed to determine the eigenvalues of interest. This is important for the determination of the PES that results from minimizing the difference between the experimental and theoretica...

Electronic spectroscopy and excited state dynamics of the Ar⋅SH complex

The laser excitation spectrum A (0,00,vS’)−X (0,00,0), has been observed for the Ar⋅SH complex. Rotational constants and bond lengths have been obtained for vibrational levels of the A and X states. A remarkable lengthening of the A state natural lifetime is observed upon Ar complexation.

Rotationally resolved B̃–X̃ electronic spectra of both conformers of the 1-propoxy radical

Five bands of the B–X laser induced fluorescence spectrum of jet-cooled 1-propoxy radical have been recorded with a spectral resolution of ≈200 MHz. The resolved rotational and fine structure of these bands has been assigned and analyzed providing rotational constants for both the X and B states as well as components of the electron spin-rotation tensor in the X state. By comparison of these constants with ones obtained from quantum chemistry calculations, two bands have been assigned to the gauche (G) conformer of 1-propoxy and 3 bands to the trans (T) conformer. The spectrum of each conformer abruptly terminates after the excitation of a single C–O stretch.

Fluorescence excitation and resolved emission spectra of supersonically cooled Al2O

The triatomic oxide Al2O was prepared by oxidation of laser vaporized aluminum, or by direct vaporization of aluminum oxide, and detected by laser induced fluorescence. The fluorescence excitation and resolved emission spectra of a transition located near 38 249 cm−1 are consistent with a linear, centrosymmetric Al–O–Al structure. Analysis of the spectrum yields an AlO bond length of 0.164 nm and values of 525 (Σ+g), 99 (Πu), and 992 cm−1 (Σ+g) for the ground state fundamental vibrations, in good agreement with theoretical predictions.

High resolution electronic spectroscopy of the R⋅SH complexes (R= Ne, Ar, Kr)

The high resolution laser induced fluorescence spectra of the A 2Σ+−X 2Π3/2 electronic transition of the R⋅SH/D (R= Kr, Ar, Ne) van der Waals (vdW) complexes are reported. Analysis of these bands requires the inclusion of rotation, fine and hyperfine structure, spin-rotation interactions, and parity splittings. A number of molecular parameters are determined, along with internuclear bond distances between the R and the SH moiety. Comparison of the present results for R⋅SH/D is made with the analogous R⋅OH/D species where applicable. In addition, the detailed “rotational” structure and the highly precise determinations of the band origins of the different heavy atom isotopomers are critical for absolute vibrational quantum number assignment in the A state.

Electronic spectroscopy of the R⋅SH (R=Ne, Ar, Kr) complexes

The laser induced fluorescence spectra of the thiohydroxyl radical inert gas complexes, R⋅SH (R=Ne, Ar, and Kr) are reported. The spectra of numerous isotopomers involving 32S, 34S, 84Kr, 86Kr, 1H, and 2H have been observed. By using isotopic shifts of the heavy atoms, and other observations, the overwhelming majority of the 60 observed vibronic transitions have been assigned as originating from the vibrationless level of the X 2Π state and terminating on specific vibrational levels (vSH, vbk, vs) of the A 2Σ+ state, where nominally vs is the R-SH stretch, vSH is the SH monomer stretch, and vbk is the bending vibration. Vibrational frequencies, ωe, and anharmonicities, ωexe, for many of the modes are obtained, as well as dissociation energies (assuming a simple model) for both the A and X states of the R⋅SH complexes.

HIGH RESOLUTION ELECTRONIC SPECTROSCOPY AND AN EMPIRICAL POTENTIAL ENERGY SURFACE FOR NE.SH/D

The high resolution, laser-induced fluorescence A 2Σ+↔X 2Π spectra of the Ne⋅SH van der Waals complex and its deuterated analog are reported. The rotational analyses provide information about the fine, hyperfine, spin–rotation, and parity interactions in these two complexes. These results are used in conjunction with measured vibrational intervals to develop an empirical potential energy surface for Ne⋅SH/D.

Characterization of the ground X̃ 2Π state of the complexes R⋅SH (R=Ne,Ar,Kr)

Information characterizing the X  2Π state of the R⋅SH (R=Ne,Ar,Kr) complexes has been obtained from two complementary experimental techniques. The spin-vibronic energy levels have been determined by wavelength resolved fluorescence spectroscopy subsequent to laser excitation of specific vibrational levels of the A 2Σ+ state. In addition, several “hot” bands from excited spin-vibronic levels of X 2Π Ne⋅SH have been observed and assigned. The experimental data have been used to construct a simple model for the ground state potential energy surface for each complex. These models show that the most stable conformation for each complex is linear H-bonded, but the barrier to isomerization to the S-bonded complex is quite low. The overall bonding is somewhat weaker and more isotropic than the corresponding hydroxyl complexes.

High resolution electronic spectroscopy of Kr⋅OH/D and an empirical potential energy surface

The high resolution laser-induced fluorescence spectra of the Kr⋅OH van der Waals complex and its deuterated analog are reported. The rotational analysis provides information about the observed fine, hyperfine, spin-rotation, and parity interactions in these two complexes. The molecular parameters allow a direct comparison with previously reported results on the analogous Kr⋅SH/D complexes. Additionally, lower resolution scans have revealed vibronic bands that have not been reported in the previous work of Fei, Zheng, and Heaven [J. Chem. Phys. 97, 1655 (1992)], while high resolution results of the 86Kr⋅OH/D, 84Kr⋅OH/D, and 82Kr⋅OH/D isomers confirmed the previous vibrational quantum number assignment. The results of the high resolution analysis are used in conjunction with measured vibrational intervals to develop an empirical potential energy surface for Kr⋅OH/D. This is compared to the recently reported potentials by Korambath et al. [J. Chem. Phys. 107, 3460 (1997)] for the other R⋅SH/D (R=Ar, Kr) com...