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We report the first direct excitation of the strongly forbidden 5s 2 1 S0 −5s5p 3 P0 transition in 87 Sr. Its frequency is 429 228 004 235 (20) kHz. A resonant laser creates a small leak in a magneto-optical trap (MOT): atoms build up to the metastable 3 P0 state and escape the trapping process, leading to a detectable decrease in the MOT fluorescence. This line has a natural width of 10 −3 Hz and can be used for a new generation of optical frequency standards using atoms trapped in a light shift free dipole trap.

An optical frequency comb generator, based on a simple electro-optic modulator in an optical resonator, can produce high-repetition-rate picosecond pulses. Unlike conventional picosecond lasers, the properties of these pulses are greatly affected by detuning the optical cavity and by dispersion caused by the electro-optic crystal. Picosecond pulses were studied in a physical device by numerical simulation and intensity autocorrelation measurements. The pulse width and pulse-to-pulse spacing were greatly affected by detuning the input laser frequency and the resonance of the optical resonator, and the numerical simulations showed that dispersion causes temporal ripples that are antisymmetric between pulse pairs.

Calculations are reported on the rotation-vibration energy levels of the arsine molecule with associated transition intensities. A potential energy surface (PES) obtained from ab initio electronic structure calculations is refined to experimental data, and the resulting energy levels display subwavenumber accuracy for all reliably known J = 0 term values under 6500 cm −1 . After a small empirical adjustment of the band centres, our calculated (J = 1 − 6) rovibrational states reproduce 578 experimentally derived energies with a root-mean-square error of 0.122 cm −1 . Absolute line intensities are computed using the refined PES and a new dipole moment surface (DMS) for transitions between states with energies up to 10 500 cm −1 and rotational quantum number J = 30.The computed DMS reproduces experimental line intensities to within 10% uncertainty for the ν 1 and ν 3 bands. Furthermore, our calculated absorption cross-sections display good agreement with the main absorption features recorded in Pacific Northwest National Laboratory (PNNL) for the complete range of 600 − 6500 cm −1 .Considering the unsuitability of the current state of AsH 3 data for either exoplanet modelling, which necessitates completeness, or industrial monitoring, which necessitates accuracy, we decided to construct a comprehensive line list for arsine which could be used for the applications mentioned above. Our approach to constructing linelists, as exploited in the ExoMol project 26,27 , uses potential energy surfaces which have been refined using spectroscopic data but ab initio dipole moment surfaces, which have J o u r n a l N a me , [ y e a r ] , [ v o l . ] , 1-15 | 1