wavenumber is directly proportional to energy. It is inversely proportional to wavelength. I think wavenumber has the unit of m-1

Wavenumber in most physical sciences is a wave property inversely related to wavelength, having SI units of reciprocal meters(m−1). Wavenumber is the spatial analog of frequency, that is, it is the measurement of the number of wavelengths per unit distance, or more commonly 2π times that, or the number of radians of phase per unit distance. Application of a Fourier transformation on data as a function of time yields a frequency spectrum; application on data as a function of position yields a wavenumber spectrum. The exact definition varies depending on the field of study. http://en.wikipedia.org/wiki/Wavenumber

wavenumber= 1/wavelength

If that is the wavelength, 31.95um is 0.003195cm. This is 313cm-1