Rotational spectrum of NSF3 in the ground and v5 = 1 vibrational states: observation of Q-branch perturbation-allowed transitions with delta(k - l) = 0, +/-3, +/-6 and anomalies in the rovibrational structure of the v5 = 1 state.

The rotational spectrum of NSF3 in the ground and v5 = 1 vibrational states has been investigated in the centimeter- and millimeter-wave ranges. R-branch (J + 1 ← J) transitions for J = 0, 1 and Q-branch rotational transitions for the v5 = 1 vibrational state have been measured by waveguide Fourier transform microwave spectroscopy in the range 8−26.5 GHz. The Q-branch transitions include 28 direct l-type doubling transitions (kl = +1, A1) ↔ (kl = +1, A2) with J ≤ 62, and 108 direct l-type resonance transitions following the selection rule Δk = Δl = ±2 with J ≤ 60 and G = |k − l| ≤ 3. A process called “regional resonance” was observed in which a cluster of levels interacted strongly over a large range in J. This process led to the observation of 55 perturbation-allowed transitions following the selection rules Δ(k − l) = ±3, ±6. In particular, (kl = +1, A+) ↔ (kl = −2, A−), (kl = +4, A+) ↔ (kl = +1, A−), (kl = +2) ↔ (kl = −1), (kl = +3) ↔ (kl = 0), (kl = +2) ↔ (kl = −3), and (kl = +3) ↔ (kl = −3). The vari...