Department of Chemistry, and the Enrico Fermi Institute THE UNIVERSITY OF CHICAGO Chicago, IL 60637, USA An Interactive Loomis-Wood Package For Spectral Assignment In Igor Pro, Version 2.0 Christopher F. Neese

What is a Loomis-Wood Plot? A fitting function, ν fit (m), is chosen to model a series in the spectrum.  ν fit (m) = ν 0 + (2B” eff + ΔB eff ) m + ΔB eff m 2 + …  m = -J” (P-branch) or J”+1 (R-branch) Each line in the spectrum is assigned a value of m based on the closest predicted line. The residuals, ν obs - ν fit (m), of the fit are plotted versus m. The Loomis-Wood plot would just be a residual plot, except that every observed line is plotted, whether it is in the series or not.

Na 2 (1,0) band F. W. Loomis and R. W. Wood, Phys. Rev. 32, (1928). Fit based on Q branch. P and R branches clearly visible as smooth curves.

History Difficult to use in initial assignment process before the advent of computer. 1960s: First computer program to generate Loomis-Wood plots.  J. F. Scott and K. N. Rao J. Mol. Spectrosc. 20, (1966) 1980s: Interactive Loomis-Wood assignment programs.  B. P. Winnewisser, J. Reinstädtler, K. M. T. Yamada, and J. Behrend, J. Mol. Spectrosc. 136, (1989).

Version 2.0 The add-in is Macintosh and Windows compatible. (Version 1.0 was not Macintosh compatible.) There is a detailed manual and a tutorial to help users get started. The add-in provides an organized line/assignment database. Lines can be assigned to multiple series. The add-in gracefully handles band heads. Multiple Loomis-Wood data sets can be created within a single Igor experiment. Multiple plots of a single Loomis-Wood data set can be created within a single Igor experiment. There is a user-extensible extract assignments feature. This feature allows the add-in to be used easily with external fitting programs. Since the add-in is written for Igor (instead of as a stand-alone program) all of Igor’s features are available to the add-in. For example, printing and graphics export are provided by Igor, not the add-in.

HCNH + Loomis-Wood More details TA02

HCNH + Loomis-Wood

C 2 H 4 Loomis-Wood

N 2 + Loomis-Wood

Acknowledgements Oka Group  Current Members: Oka Jennifer Gottfried Chris Morong Aaron Schoeffler  Former Members: Dan Hullah Mike Lindsay Ben McCall Chris Tarsitano Norman Craig