Millimeter-wave spectroscopy of vibrationally-excited NaCCH ((X)over-tilde(1)Sigma(+)) and MgCCH ((X)over-tilde(2)Sigma(+)): the nu(5) bending mode

Pure rotational spectra of NaCCH ((X) over tilde(1)Sigma(+)) and MgCCH ((X) over tilde(2)Sigma(+)) have been recorded in their ground state and nu(5) vibrational level, the metal-C-C bend, in the range 315-525 GHz using milli meter-wave direct absorption techniques. This data set complements previous measurements. For NaCCH, rotational transitions were recorded for nu(5)(l) = 0(0), 1(1), 2(2), 2(0), 3(3), and 4(4) levels, and for the 0(0) states o f NaCCD and (NaCCH)-C-13. Transitions originating in the 1(1), 2(0), and 2( 2) states of MgCCH were additionally observed. Rotational, I-type doubling, and vibration-rotation parameters have been determined for both species, a s well, as estimates of the omega(5) bending frequency. (C) 1999 Elsevier S cience B.V. All rights reserved.