High resolution rovibrational spectroscopy of pyrimidine: Analysis of the B1 modes ν10b and ν4 and B2 mode ν6b

We report the first high resolution rovibrational analysis of the infrared spectrum of pyrimidine (C4H4N2) based on measurements using our Fourier transform spectrometer, the Bruker IFS 125 HR Zürich Prototype (ZP) 2001. Measurements were conducted at room temperature in a White-type cell with effective optical path lengths between 3.2 and 9.6 m and with resolutions ranging from 0.0008 to 0.0018 cm−1 in the region between 600 and 1000 cm−1. The spectrum was analyzed in the ν4 (ν˜0=718.5411cm-1), ν10b (ν˜0=803.97948cm-1) and ν6b regions of pyrimidine (ν˜0=620.54970cm-1) using an effective Hamiltonian. A total of about 15 000 rovibrational transitions were assigned. The root mean square deviations of the fitted data are in the ranges drms = 0.00018-0.00024 cm−1, indicating an excellent agreement of experimental line data with the calculations. The results are discussed briefly in relation to possible extensions to spectra of DNA bases and to intramolecular vibrational redistribution at higher energy. The analysis of the ν10b and ν4 bands will also be useful in the interstellar search for pyrimidine in the infrared region.