Fig. 4: Illustration of the SNAPS procedure in operation for the highest-degree P = 1 hub of H216O.
From: All paths lead to hubs in the spectroscopic networks of water isotopologues H216O and H218O
The general terms and symbols utilized are defined in the central panel of Fig. 1. Panel a contains two disjoint paths from (0 0 0)10,1 to (0 1 0)42,3, p1 and p2, where the lines are denoted with solid and dashed arrows, respectively. For the transitions and the states of panel a, the same formalism is adopted as in Fig. 3. The numbers on the arrows are wavenumbers in cm−1, with the 1σ uncertainties of the last digits in parentheses. The boldfaced values were observed during this study, whereas the other two wavenumbers are taken from ref. 36. Relying on p1 and p2, two independent estimates can be derived for the (0 1 0)42,3 relative energy, which are presented in the violet box of panel a. In fact, p1 and p2 form a 12-membered cycle with a discrepancy of 5.1(50) × 10−7 cm−1 [15.4(151) kHz]. For technical details on the determination of relative energies and discrepancies, Eqs. (1–5). Panel b presents two typical Lamb dips, a regular and an inverted profile, recorded with our NICE-OHMS apparatus. To aid their comparison, both spectra are mapped onto the \(({I}_{\min }-I)/{I}_{\min }\) intensity scale, where I means the intensity at a detuning point for a particular line, and \({I}_{\min }\) is the lowest intensity in the ± 2 MHz detuning region. As documented in ref. 41, inverted profiles occur for transitions with large (>0.1 s−1) Einstein-A coefficients.
