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Sub-Doppler spectra of the A 3Π–X 3Σ−(0,0) and (1,0) bands of the PH radical have been recorded using an injection seeded single mode optical parametric oscillator in a supersonic jet expansion. Most of the rotational lines in these laser-induced fluorescence spectra exhibit clear splittings or asymmetry due to hyperfine structure. An analysis of this structure is presented in terms of the electronic structure and bonding of the molecule. Comparisons are drawn with the corresponding A 3Π state of the NH radical, and some shortcomings in the accepted methods for interpretation are highlighted and discussed.

We describe the construction of an all solid-state, narrow bandwidth, pulsed optical parametric oscillator (OPO) based on β-barium borate nonlinear crystals. The OPO was injection seeded by an external cavity diode laser in the range 755–855 nm to generate high power narrow bandwidth tunable light in this range and simultaneously at 606–669 nm. The bandwidth of the visible light was ∼130 MHz, and after frequency doubling or sum frequency mixing with the second harmonic of the pump Nd:YAG laser, sub-Doppler spectra with an overall resolution of 450 MHz were taken in the UV. The system is demonstrated by taking high-resolution spectra of the v′=2–3 and 5–7 bands of the A 3Π–X 3Σ−(v′,0) progression and the v′=4–v″=0 band of the d 1Π–a 1Δ transition in PF. These spectra show clear hyperfine structure, and an analysis of this structure is presented and interpreted in terms of the electronic structure of the molecule. As a prelude to this high-resolution study, the first ten members of the A–X band system and t...

Sub-Doppler laser induced florescence spectra were recorded of a selection of bands within the A (2)Sigma(+)-X (2)Pi and B (2)Pi-X (2)Pi transitions of NCO in a supersonic molecular beam. The light source was a diode seeded optical parametric oscillator, which gave an effective resolution of 0.01 cm(-1) in the ultraviolet. Analysis of the A (2)Sigma(+)-X (2)Pi transition at high resolution allowed fitting of both the fine and hyperfine structures, and a set of rotational and hyperfine constants were obtained for 13 vibronic levels within the A (2)Sigma(+) state including levels of both (2)Sigma(+) and (2)Pi vibronic characters. Analysis of the 0(0) (0) and 1(0) (1) bands of the B (2)Pi-X (2)Pi transition, together with a band from the A (2)Sigma(+) state at the same energy, was also performed. These did not reveal any hyperfine structure although the resolution was the same as the work at lower total energy, and this observation is discussed. Refined rotational constants and perturbation parameters for the interaction between the A and B states were also obtained.

Investigations of the hyperfine structure in the excited electronic states of several free radical species have revealed shortcomings in the currently accepted values used for the theoretical interpretation of such interactions. We introduce updated reference atomic values from a combination of experimental observations and ab initio calculations. The latter are at Hartree-Fock and multireference configuration interaction levels of theory and several atomic test cases are discussed. Furthermore, ground and excited electronic state hyperfine coupling constants are calculated using both levels of theory for a range of first- and second-row diatomic hydride and nonhydride radicals. These results, together with a selection of other experimental measurements are then compared with experimental data where available, and the implications of the revised interpretation are discussed.

Sub-Doppler laser induced florescence spectra were recorded of a selection of bands within the A Σ2+−X Π2 and B Π2−X Π2 transitions of NCO in a supersonic molecular beam. The light source was a diode seeded optical parametric oscillator, which gave an effective resolution of 0.01 cm−1 in the ultraviolet. Analysis of the A Σ2+−X Π2 transition at high resolution allowed fitting of both the fine and hyperfine structures, and a set of rotational and hyperfine constants were obtained for 13 vibronic levels within the A Σ2+ state including levels of both Σ2+ and Π2 vibronic characters. Analysis of the 000 and 101 bands of the B Π2−X Π2 transition, together with a band from the A Σ2+ state at the same energy, was also performed. These did not reveal any hyperfine structure although the resolution was the same as the work at lower total energy, and this observation is discussed. Refined rotational constants and perturbation parameters for the interaction between the A and B states were also obtained.