Spectroscopy of the formaldehyde isotopomer (H2CO)-C-13 in the microwave to terahertz region

The pure rotational spectrum of (H2CO)-C-13 in its ground vibrational state has been investigated extensively between 8 and 1900 GHz using samples of natural isotopic abundance as well as samples enriched in C-13. The accurate new line frequencies were subjected to a combined fit with previously published data, resulting in distinctly improved spectroscopic constants, which include several octic and one decic centrifugal distortion constants. Fits employing Watson's S and A reductions will be compared. The following rotational constants have been obtained: A(S)=281993.0397 (31), B-S=37809.106966 (213), C-S=33215.941417 (207) and A(A)=281993.0148 (32), B-A=37811.090040 (219), C-A=33213.976745 (207) MHz, respectively.