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Stimulated-emission pumping spectra were recorded for many pure bending levels [(0, 2, 0)–(0, 34, 0)] and bend–symmetric-stretch combination levels [(1, 0, 0)–(1, 8, 0) and (3, 4, 0)–(3, 8, 0)] in the X˜^1Σg+ state of C_3 following excitation of transitions in the A˜^1Π_u−X˜^1Σg+ band system. Rotational levels to J = 16 were probed and, because of strong mixing of vibrational angular momentum components, levels with l up to 8 were observed. A rotational analysis was carried out by means of a simple rigid-rotor harmonic-oscillator model for a linear molecule. An adequate fit was obtained, showing that all these vibrational levels could be described by a linear average geometry even though the bending vibration is known to be of extremely large amplitude. Bυ was found to increase strongly with υ_2 and to decrease with excitation in ν_1. Interpretation of the physical meaning of the resulting parameters is difficult, however, since the vibrational potential is not well described by a harmonic oscillator.

Twenty vibration–rotation lines in the bending fundamental of HN_2^+ have been detected by absorption spectroscopy using a tunable-diode laser. The ions were produced in a large hollow-cathode discharge in a mixture of hydrogen and nitrogen maintained at liquid-nitrogen temperature. Analysis of the spectrum provides an accurate determination of the ν_2 band origin and the major parameters describing the (01 ^10) state of the ion.

We report the detection of 13 rotational transitions in the first excited bending state (010) of CD_2 using the technique of far-infrared laser magnetic resonance spectroscopy. Molecular parameters for this state are determined from these new data together with existing infrared observations of the ν_2 band. Additional information on the ground vibrational state (000) is also provided by the observation of a new rotational transition, and this is combined with existing data to provide a refined set of molecular parameters for the CD_2 ground state. One spectrum has been observed that we assign as a rotational transition within the first excited symmetric stretching state (100) of CD_2. These data will be of use in refining the structure and the potential function of the methylene radical.

Stimulated-emission pumping spectra were recorded for many pure bending levels [(0, 2, 0)−(0, 34, 0)] and bend-symmetric-stretch combination levels [(1, 0, 0)−(1, 8, 0) and (3,4, 0)−(3, 8, 0)] in the X˜^1Σ_g^+ state of C_3 following excitation of transitions in the Ã^1II_u−X˜^1Σ_g^+ Rotational levels to J = 16 were probed and, because of strong mixing of vibrational angular momentum components, levels with l up to 8 were observed. A rotational analysis was carried out by means of a simple rigid-rotor harmonic-oscillator model for a linear molecule. An adequate fit was obtained, showing that all these vibrational levels could be described by a linear average geometry even though the bending vibration is known to be of extremely large amplitude. B_v was found to increase strongly with v_2 and to decrease with excitation in v_1. Interpretation of the physical meaning of the resulting parameters is difficult, however, since the vibrational potential is not well described by a harmonic oscillator.

Five transitions in neutral atomic helium involving single-electron-excited S, P, and D levels with n = 3 to 8 and Δn = 0 and 2 have been measured in the mid- and far-infrared regions by using tunable-diode-laser sources. The accuracies of the relevant intervals have thus been improved by a factor of approximately 10 with respect to previous optical measurements. These results should be of use in refining the determination of helium energy levels.

Five transitions in neutral atomic helium involving single-electron-excited S, P, and D levels with n = 3 to 8 and Δn = 0 and 2 have been measured in the mid- and far-infrared regions by using tunable-diode-laser sources. The accuracies of the relevant intervals have thus been improved by a factor of approximately 10 with respect to previous optical measurements. These results should be of use in refining the determination of helium energy levels.