Sub-Doppler and Doppler spectroscopy of DCN isotopomers in the terahertz region: ground and first excited bending states ( v1v2v3)=(0 1 e, f 0)

Abstract

The rotational spectra of the deuterium cyanide isotopic species DCN, D 13CN, DC 15N, and D 13C 15N were recorded in the vibrational ground and first excited bending state ( v 2=1) up to 2 THz. The R-branch transitions from J=3←2 to J=13←12 were measured with sub-Doppler resolution. These very high resolution (∼70 kHz) and precise (±3–10 kHz) saturation dip measurements allowed for resolving the underlying hyperfine structure due to the 14N nucleus in DCN and D 13CN for transitions as high as J=10←9. Additional high J R-branch ( J=25←24 to J=28←27) transitions around 2 THz and direct l-type (Δ J=0, J=19 to J=25) transitions from 66 to 118 GHz were recorded in Doppler-limited resolution. For the ground state of D 13C 15N, the J=1←0 transition was measured for the first time. The transition frequency accuracies for the other deuterated species were significantly improved. These new experimental data, together with the available infrared rovibrational data and previously measured direct l-type transitions, were subjected to a global least squares analysis for each isotopomer. This yielded precise sets of molecular constants for the ground and first excited vibrational states, including the nuclear quadrupole and magnetic spin–rotation coupling constants of the 14N nucleus for DCN and D 13CN. The hyperfine structure due to the D, 13C, and 15N nuclei have not been resolved, but led to a broadening of the observed saturation dips.