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With new astronomical infrared spectrographs the demands of accurate atomicdata in the infrared have increased. In this region there is a large amount ofparity-forbidden lines, which are of importance in diagnostics of low-densityastrophysical plasmas. We present improved, experimentally determined, energylevels for the lowest even LS terms of Fe II, Ti II and Cr II, along withaccurate Ritz wavelengths for parity-forbidden transitions between and withinthese terms. Spectra of Fe II, Ti II and Cr II have been produced in a hollowcathode discharge lamp and acquired using high-resolution Fourier Transform(FT) spectrometry. The energy levels have been determined by using observedallowed ultraviolet transitions connecting the even terms with upper odd terms.Ritz wavelengths of parity-forbidden lines have then been determined. Energylevels of the four lowest Fe II terms (a$^{6}$D, a$^{4}$F, a$^{4}$D anda$^{4}$P) have been determined, resulting in 97 different parity-forbiddentransitions with wavelengths between 0.74 and 87 micron. For Ti II the energylevels of the two lowest terms (a$^{4}$F and b$^{4}$F) have been determined,resulting in 24 different parity-forbidden transitions with wavelengths between8.9 and 130 micron. Also for Cr II the energy levels of the two lowest terms(a$^{6}$S and a$^{6}$D) have been determined, in this case resulting in 12different parity-forbidden transitions with wavelengths between 0.80 and 140micron.Comment: Accepted for publication in A&A, 13 pages, 6 figures, 9 table

Accurate Ritz wavelengths of parity-forbidden [$\ion{Fe}{ii}$], [$\ion{Ti}{ii}$], and [$\ion{Cr}{ii}$] infrared lines of astrophysical interest