The high resolution rovibrational spectrum of H2S has been evaluated from three-dimensional ab initio potential energy and electric dipole moment functions and variational rovibrational eigenfunctions, which took full account of anharmonicity effects and rotation–vibration coupling. The quality of the near equilibrium theoretical potential energy function has been checked by comparisons with experimental equilibrium structure, empirical quartic force fields, vibrational band origins, centrifugal distortion constants, and rotational energy levels. All parameters agree well with the available experimental data. Vibrational band intensities for the ν2, 2ν2, ν1, and ν3 bands have been calculated from empirical and ab initio dipole moment functions and compared with experimental and theoretical integrated band intensities. The difficulties arising by the derivation of such data from the experimental intensities of H2S are discussed. The theoretical results strongly suggest that higher than first derivatives are needed for a proper description of the dipole moment function. The room temperature absorption spectra have been evaluated ab initio for the pure rotational and the ν2, 2ν2, ν1, and ν3 transitions. The unusual intensity pattern of the P, Q, and R branches attributed to the rotational–vibrational coupling has been well reproduced. Absolute line intensities calculated previously by perturbation theory are compared with variational results. The purely theoretical line intensities agree satisfactorily with experiment for the bending transitions, however, the extremely flat regions of the dipole moment functions along the bond stretching displacements make the transition intensities very sensitive to the values of the dipole moment derivatives.

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Potential energy surfaces and spectroscopic properties were calculated for H2S and H3S+ from highly correlated SCEP-CEPA wave functions. The equilibrium geometry of H3S+ is predicted to be re =1.350 Å and θe =32.2°. The vibrational frequencies of H323S+ (in cm−1) were calculated to be 2529 (ν1), 1050 (ν2), 2527 (ν3), and 1208 (ν4) which are all in close agreement with experimental values obtained for solid H3S+SbF−6. The computed proton affinity for H2S of PA298=716.7 kJ mol−1 is in very good agreement with experiment.

Potential energy, electric dipole, and electronic transition moment functions have been calculated for several bound electronic states of CH− and NH− from accurate electronic wave functions. Spectroscopic constants for the X 2Π state of NH− have been compared with the data recently obtained by laser induced autodetachment spectroscopy. Spectroscopic constants of the A 2Σ+ state of NH− and radiative X 2Π–A 2Σ+ transition probabilities are presented. Spectroscopic constants and infrared transition probabilities for the X 3Σ− and the a 1Δ states of CH− have been calculated. The radiative lifetime of v=1 in CH−(X 3Σ−) is found to be in a very good agreement with a recent experimental value. The transition probabilities are for both ions much larger than those of their neutral counterparts, and increase in the series OH−, NH−, CH−.

The near-equilibrium potential energy surface of H2Br+ was calculated by SCEP-CEPA using a basis set of 82 contracted GTOs. The equilibrium geometry is predicted to be re=1.441 Å and αe=92.1°. Vibrational frequencies were calculated variationally and the fundamentals of H279Br+ (in cm−1) are ν1=2403, ν2=1073, and ν3=2398. An unusual isotopic effect, due to vibrational anharmonicity, is discussed. The calculated proton affinity of HBr of 587 kJ mol−1 is in excellent agreement with experimental values.