Rotational analysis of the 2ν₅ band of Formaldehyde

This is an example of a complicated problem, involving several interacting states. The work is described in S. Saha, H. Barry, G. Hancock, G. A. D. Ritchie and C. M. Western, Mol. Phys. 105, 797 (2007), doi:10.1080/00268970601126767, and a full set of PGOPHER files for this work is available in the supplementary data for this paper in the University of Bristol data repository at doi:10.5523/bris.1sn5ke0b7d2j81u81tsxwki7sx.

The data file, HCHO_2nu5.pgo, is structured with one manifold for the ground state, and one manifold containing the excited vibrational state of interest (v5=2 in the tree on the left). Also in the excited state manifold are the vibrational states the v5=2 state interacts with, such as those labelled 345 and 2346 on the left, and the perturbations between them, such as <v5=2|bc|2346>. Only some of the states are shown in the model on the left; the data file actually includes 28 states and 21 perturbations.

The supplementary data also includes the observed linelist used to generate this file; points to note about this file include

the use of an include directive, so the overall linelist is contained in 12 separate files
the use of the quantumnumberformat directive so that all J values are doubled in the file. (This reflects historical usage, and would probably not be done on new files.)
the use of a Parameter statement to constrain selected band origins and rotational constants. (Note that, in the file as saved, a pair of OverrideWeight 0/OverrideWeight directives has been used to exclude these temporarily from the fit.)

Rotational analysis of the 2ν5 band of Formaldehyde

Rotational analysis of the 2ν₅ band of Formaldehyde