Molecule Types Vibrational Structure Force Field Analysis Samples | <Prev Next> |

The files listed below reproduce the fits given
in Table 1a and Table 1b of L. Hedberg and I. M. Mills, J.
Molec. Spectrosc.** 203**, 82 (2000). The files are:

- C2H2ff.obs - the observed quantities for the fit for use with either of the files below. Points to note:
- Several different (equivalent) ways are used to specify the parameters.
- The
^{13}C vibrational frequencies are fitted as isotope shifts, as these are typically more accurate than absolute values. - Different weights (estimated errors ) are used for the
observed values for C
_{2}D_{2}, in line with the original paper.

- C2H2emp.pgo - a fit to
purely empirical symmetry force constants.

- C2H2scaled.pgo - a fit
scaling
*ab initio*force constants to match experiment.

Notes on the data files:

- The force constants are expressed in symmetry co-ordinates, rather than internal valence coordinates.
- The two degenerate bending modes are repeated with the same
force constant, so F4 and F6 appear twice in the force constant
list.

- The
*z*matrix, shown below, uses Cartesian coordinates to specify the atomic positions, and has two dummy atoms to allow the bending modes to be uniquely specified.