The error of photoionization cross-section of target species mainly comes from the error caused by Di, Si, and Xi, for which the error of Di is about 20%, the error of Si is about 2% under the current signal -to-noise ratio, and the error caused by Xi can be ignored under the action of the flow controller. According to the relative error transfer formula, the photoionization cross-sections measured in the experiment are expected to have an error of ±20%. The studied molecules and experimental parameters used in this work are shown in Table , all the target molecules in this work have sufficient saturated vapor pressure, so they do not need to be dissolved in other reagents. The total flow rate in the flow reactor was 500 SCCM (standard cubic centimeter per minute), the concentration of the tested speciesbenzonitrile (MACKLIN,99%), o-cyanotoluene (MACKLIN,98%), mcyanotoluene (MACKLIN,99%), and p-cyanotoluene (MACKLIN,99%)-was 1‰, the concentration of NO as the reference species wa s 4%, the experiment was carried out under the pressure of 4 Torr and the rest was argon. All chemicals were used without further purification.