Absorption cross section of gas phase isoprene in the infrared-visible range

We have recorded the gas phase spectrum of isoprene at room temperature from the mid-infrared range and into the visible range (600 cm^-1 to 17050 cm^-1). Absorption spectra were obtained by Fourier transform infrared, conventional dispersion ultraviolet-visible-near-infrared and cavity ring-down spectroscopy to cover the entire range with a resolution comparable to that of the instruments on the James Webb Space Telescope. We have assigned the CH-stretching fundamental and overtone bands corresponding to the Δv_CH=1-6 transitions based on anharmonic vibrational calculations using normal mode and local mode models, for the lower- and higher-energy regions, respectively. We have determined accurate absolute intensities of the observed CH-stretching regions and compare with existing experimental values and with theoretical results. The accuracy of our absolute band intensity is about 2% in the fundamental region and about 10% in the 6 orders of magnitude weaker highest overtone region. Our spectrum can facilitate the detection and possibly quantification of isoprene in planetary atmospheres.