The 101–000 and 202–101 rotational transitions of HC35Cl and HC37Cl in the X̃ 1A′ ground vibronic state have been observed with a Fourier transform millimeter-wave spectrometer. The HCCl molecule is produced by discharging a gaseous sample of CH2Cl2 diluted in Ar with a pulsed discharge nozzle. The effective rotational constant (B+C)/2, the centrifugal distortion constant ΔJ, the nuclear quadrupole interaction constants, and the nuclear-spin rotation interaction constant are determined for each isotopic species. The nuclear-spin rotation interaction is found to make a significant contribution to the hyperfine structure of this molecule, which originates from the relatively low-lying electronic excited state. The nuclear quadrupole interaction tensor is highly asymmetric, indicating a significant π character of the C–Cl bond. This can be interpreted in terms of the backdonation of π electrons from the chlorine atom to the carbon atom.
The a-type R-branch K−1=0 rotational transitions of the HCS and DCS radicals have been measured in the frequency range of 161 to 644 GHz using source modulation spectrometers. For DCS, the seven fine and hyperfine components of the 101–000 rotational transition are also measured at 35 GHz using a Fourier transform millimeter-wave spectrometer. The spectra are found to be perturbed by the K−1=1 state through the off-diagonal spin–rotation interaction (εab+εba)(NaSb+SbNa+NbSa+SaNb). In particular for DCS, strong perturbations are observed. The rotational constants, A, B+C, and B−C, of DCS are determined through an analysis of the perturbation. The r0 structure of HCS has been determined as follows: r0(CH)=1.079(3) Å, r0(CS)=1.562 28(3) Å, and α0(HCS)=132.8(3)°. The quasilinearity parameter, γ0, is evaluated to be 0.80 for DCS, indicating that HCS is not a simple bent molecule.
The hyperfine resolved rotational spectrum of the CH2CP radical in the X̃ 2B1 ground electronic state has been observed for the first time using a Fourier transform microwave spectrometer in combination with a pulsed discharge nozzle. The radical was produced by discharging a mixture of PH3 and C2H2 diluted in either Ar or Ne. A total of 25 hyperfine components of the 202–101 and 303–202 transitions have been measured which enabled us to precisely determine hyperfine coupling constants for both phosphorus and hydrogen nuclei. Spin densities on the phosphorus and β-carbon atoms, estimated from the hyperfine coupling constants, suggest that the radical forms an allenic structure (CP double bond) that is modified by a phosphoryl structure (CP triple bond), which is consistent with the theoretical estimation obtained previously by an ab initio calculation. The nature of the CP chemical bond in the radical is investigated in comparison with the corresponding nitrogen bearing counterparts.
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