An spectroscopic model of the molecular oxygen atmospheric and infrared bands.

We present a unified variational treatment of the magnetic dipole matrix elements, Einstein coefficients and line strength for general open-shell diatomic molecules in the general purpose diatomic code Duo. Building on previous work in which similar expressions for the electric quadrupole transitions were developed, we also present a complete spectroscopic model for the infrared, electric dipole-forbidden, spectrum of the O molecule. The model covers seven states, namely the X Σ-g, a Δ, b Σ+g, I Π, II Π, I Π and II Π states, for which 7 potential energy, 6 electronic angular momentum, 7 spin-orbit, and 14 quadrupole moment curves are calculated using ic-MRCI theory and an aug-cc-pV5Z basis set.

The infrared absorption spectrum of radioactive water isotopologue HO.

A room temperature line list for the HO radioactive isotopologue of the water molecule is computed using the variational nuclear-motion DVR3D program suite and an empirical high-precision potential energy function. The line list consists of rotation-vibrational energies and Einstein-A coefficients, covering a wide spectral range from 0 to 25000 cm and the total angular momenta J up to 30. Estimates of air-broadening coefficients are provided.

A semi-classical approach to the calculation of highly excited rotational energies for asymmetric-top molecules.

We report a new semi-classical method to compute highly excited rotational energy levels of an asymmetric-top molecule. The method forgoes the idea of a full quantum mechanical treatment of the ro-vibrational motion of the molecule. Instead, it employs a semi-classical Green's function approach to describe the rotational motion, while retaining a quantum mechanical description of the vibrations.

Communication: Tunnelling splitting in the phosphine molecule.

Splitting due to tunnelling via the potential energy barrier has played a significant role in the study of molecular spectra since the early days of spectroscopy. The observation of the ammonia doublet led to attempts to find a phosphine analogous, but these have so far failed due to its considerably higher barrier. Full dimensional, variational nuclear motion calculations are used to predict splittings as a function of excitation energy.