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Determine B rotational constants for the donor twist overtone (Ka = 1) and improve upper-state B values for the 2753.9 cm−1 band

Determine the ground-state B rotational constants for the donor twist overtone (DT2) intermolecular mode of (D2O)2 for Ka = 1 levels and obtain precise upper-state B constants for the 2753.9 cm−1 combination band, which are currently not known or not well determined experimentally.

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Background

Evaluating band assignments by additivity of alpha values requires reliable rotational constants for both ground- and excited-state intermolecular modes; however, key parameters for the donor twist overtone at Ka = 1 are missing.

The lack of precise upper-state constants for the weak 2753.9 cm−1 band further limits quantitative tests and comparison with theoretical models.

References

However, in the case of the 2753.9 cm-1 band, the test is not very useful because the upper state B-values are not well determined experimentally and those for the donor twist overtone in the ground state are not known for Ka= 1.

— Spectra of the D2O dimer in the O-D fundamental stretch region: the acceptor symmetric stretch fundamental and new combination bands (2402.14923 - Barclay et al., 22 Feb 2024) in Section III.B (Combination Bands)