Toward an improved understanding of the AsH2 free radical: laser spectroscopy, ab initio calculations, and normal coordinate analysis.

Spectra of the Ã(2)A(1)-X̃(2)B(1) transition of the jet-cooled AsD(2) and AsHD isotopologues of the arsino radical have been studied by laser induced fluorescence and wavelength resolved emission techniques. A high-resolution spectrum of the AsD(2) 0(0)(0) band has been recorded, and an improved r(0) structure [r(0)(') = 1.487(4) Å, θ(0)(') = 123.0(2)°] for the à state has been determined from the rotational constants. To aid in the analysis of the vibrational levels, an ab initio potential energy surface of the X̃(2)B(1) state has been constructed and the rovibronic energy levels of states on that potential have been determined using a variational method. The vibrational levels observed in wavelength resolved emission spectra have been fitted to a local mode Hamiltonian with most anharmonic parameters fixed at ab initio values, and the resulting harmonic frequencies have been used to perform a normal coordinate analysis which yielded an improved set of quadratic force constants and an estimate of the equilibrium ground state structure.

Heavy atom nitroxyl radicals. V. An experimental and ab initio study of the previously unknown H2PS free radical.

The B̃(2)A(')-X̃(2)A(') transition of the prototypical thiophosphoryl radical, H(2)PS, was observed for the first time using laser-induced fluorescence and single vibronic level emission spectroscopy. H(2)PS and its deuterated isotopologues, D(2)PS and HDPS, were produced in a pulsed supersonic discharge jet from a precursor mixture of Cl(3)PS and H(2) or D(2) or an H(2)/D(2) mixture in high-pressure argon. High level ab initio calculations of the lowest three doublet electronic states helped in the definitive assignment of the B̃-X̃ transition, which involves electron promotion from the π to the π∗ orbital. Vibrational frequencies were determined for several modes of each isotopologue in the X̃ and B̃ states and found to be in accord with theoretical predictions. Although a line-by-line rotational analysis was not possible, the observed band contours are consistent with the geometries obtained from our ab initio calculations. Theory indicates that PS bond length increases upon electronic excitation, while the pyramidalization of the radical does not change significantly.

Electronic spectroscopy of the jet-cooled arsenic dicarbide (C2As) free radical.

The (2)Delta(r)-X (2)Pi(r) band system of the jet-cooled arsenic dicarbide (C(2)As) free radical has been recorded by laser-induced fluorescence (LIF) techniques in the 685-588 nm region. The radical was produced in a pulsed electric discharge jet using a precursor mixture of AsCl(3) vapor and methane in high pressure argon. A series of weak bands involving all three excited state vibrations was observed for both (12)C(2)As and (13)C(2)As. High-resolution spectra of the (2)Pi(12) component of the 0(0)(0) bands of both isotopomers were rotationally analyzed, leading to the conclusion that the upper state is (2)Delta with a small spin-orbit splitting (A = 2.78 cm(-1)). Ground and excited state molecular structures of r(0)(")(CC,ab initio) = 1.2933 A, r(0)(")(CAs) = 1.734(4) A and r(0)(')(CC,ab initio) = 1.2276 A, r(0)(')(CAs) = 1.830(3) A were derived from the B values and our density functional predictions of the C-C bond lengths. Single vibronic level emission spectra were recorded for many of the LIF bands and these were used to obtain the ground state vibrational frequencies and spin-orbit splittings. These data were satisfactorily fitted to a Renner-Teller model which gave (12)C(2)As parameters of epsilon = 0.695(8), omega(1) = 1704.8(20) cm(-1), omega(2) = 161.6(8) cm(-1), omega(3) = 663.6(12) cm(-1), and a spin-orbit constant A = 857.7(11) cm(-1).