Rotational Spectrum of NSF3 in the Ground and v5 = 1 Vibrational States: Observation of Q-Branch Perturbation-Allowed Transitions with Δ(k − l) =

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• 作者：Sven Macholl ; Heinrich Mder ; Hauke Harder ; Laurent Marguls ; Pascal Dran ; Jean Coslou ; Jean Demaison ; Petr Pracna
• 刊名：Journal of Physical Chemistry A
• 出版年：2009
• 出版时间：January 29, 2009
• 年：2009
• 卷：113
• 期：4
• 页码：668-679
• 全文大小：243K
• 年卷期：v.113,no.4(January 29, 2009)
• ISSN：1520-5215

文摘

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 various aspects of the regional resonances are discussed in detail. An accidental near-degeneracy of the kl = 0 and kl = −4 levels at J = 26/27 led to the observation of perturbation-allowed transitions following the selection rule Δ(k−l) = ± 6 with (kl = +2) ↔ (kl = −4). A corresponding near-degeneracy between kl = −1 and kl = −3 levels at J = 30/31 led to the detection of similar transitions, but with (kl = +3) ↔ (kl = −3). In the range 230−480 GHz, R-branch rotational transitions have been measured by absorption spectroscopy up to J = 49 in the ground-state and up to J = 50 in the v₅ = 1 vibrational state. The transition frequencies have been analyzed using various reduced forms of the effective Hamiltonians. The data for the v₅ = 1 vibrational state have been fitted successfully using two models up to seventh order with Δk = ±3 interaction parameters constrained (d_t constrained to zero, and ε to zero or to the ground-state value). On the other hand, reductions with the (Δk = ±1, Δl = 2) interaction parameter q₁₂ fixed to zero failed to reproduce the experimental data since the parameters defining the reduction transformation do not arise in the correct order of magnitude. The ground-state data have been analyzed including parameters up to fourth order constraining either parameters of the Δk = ± 3 interactions to zero (reduction A), or of the Δk = ±6 interactions to zero (reduction B). The unitary equivalence of the different parameter sets obtained is demonstrated for both vibrational states.