Rotational spectra of the deuterated carbon chain molecules: C3D, C4D, C3HD, and C4HD

The rotational spectra of the deuterated carbon chain molecules, C3D, C4D, C3HD, and C4HD, have been measured with the Fourier transform microwave (FTMW) spectrometer. The C3D and C4D radicals are produced by discharging the DCCD gas diluted in Ar. On the other hand, the gaseous mixture of HCCH, DCCD, and HCCD diluted in Ar is used for producing C3HD and C4HD. For C3D, the molecular constants are determined from a joint least-squares analysis with the previously published millimeter- and submillimeter-wave data by considering the vibronic interaction between the 2Π ground state and the low-lying 2Σ vibronic state. The molecular constants of C4D are determined by use of the conventional Hamiltonian of the 2Σ radical, while the effective rotational constant and centrifugal distortion constant are derived for C3HD and C4HD. In the present study, the hyperfine interaction constants of the deuterium nuclei in C3D and C4D are determined accurately. In particular, the nuclear quadrupole interaction constant, eQq, of the C3D radical is found to be significantly smaller than those of C2D and C4D, indicating that C3D has a floppy motion of the CCD bending mode due to the large Renner-Teller effect.