Rotational spectra of vibrationally excited CCH and CCD.
The millimeter-wave rotational spectra of the lowest bending and stretching vibrational levels of CCH and CCD were observed in a low pressure discharge through acetylene and helium. The rotational, centrifugal distortion, and fine structure constants were determined for the (02(0)0) and (02(2)0) bending states, the (100) and (001) stretching levels, and the (011) combination level of CCH. The same pure bending and stretching levels, and the (110) combination level were observed in CCD. Apparent anomalies in the spectroscopic constants in the bending states were shown to be due to l-type resonances. Hyperfine constants, which in CCH are sensitive to the degree of admixture of the A 2Pi excited electronic state, were determined in the excited vibrational levels of both isotopic species. Theoretical Fermi contact and dipole-dipole hyperfine constants calculated by Peric et al. [J. Mol. Spectrosc. 150, 70 (1991)] were found to be in excellent agreement with the measured constants. In CCD, new rotational lines tentatively assigned to the (100) level largely on the basis of the observed hyperfine structure support the assignment of the C-H stretching fundamental (nu1) by Stephens et al. [J. Mol. Struct. 190, 41 (1988)]. Rotational lines in the excited vibrational levels of CCH are fairly intense in our discharge source because the vibrational excitation temperatures of the bending vibrational levels and the (110) and (011) combination levels are only about 100 K higher than the gas kinetic temperature, unlike the higher frequency stretching vibrations, where the excitation temperatures are five to ten times higher.
Millimeterwave spectroscopy of active laser plasmas; the excited vibrational states of HCN
Millimeter and submillimeter microwave techniques have been used for the spectroscopic study of an HCN laser plasma. Forty‐seven rotational transitions in 12 excited vibrational states have been observed. Numerous rotational, vibrational, and perturbation parameters have been calculated from these data. A discussion of experimental techniques is included.
Ã 2Π←X̃ 2Σ+ infrared electronic transition of C2H
Five bands of the A 2Π←X 2Σ+ lowest electronic transition of C2H have been observed in the region 3600–4200 cm−1 in an argon discharge over polyacetylene using color center laser spectroscopy with magnetic rotation sensitivity enhancement. The band origins are approximately 3692, 3773, 3785, 4011, and 4106 cm−1. Rotational assignments and preliminary fittings of all five bands have been made. Four of the bands have a 2Σ+ lower vibronic state which is undoubtedly the ground vibronic state of the molecule, and different 2Π upper vibronic states which correspond to mixtures of the lowest vibronic state of the A electronic state and three different vibrationally excited levels of the X electronic state with an odd number of quanta in the bending mode and overall 2Π symmetry. These three ground state vibrational levels have been tentatively assigned as (1,1,0), (0,1,2), and (0,5,1). The four 2Π vibronic levels are mixed by vibronic coupling between the X and A electronic states thereby providing electron...