Abstract
The time-of-flight mass spectrum (TOFMS) relative to the resonant two-photon ionization of gas phase p-dichlorobenzene was obtained in the wavelength range of 240-250 nm by a home-made system. A special design was made to reduce the effect of memory on the inner wall of the sample inlet system suitable for the investigation of semi-volatile organic compound. In this wavelength range, p-dichlorobenzene molecules firstly absorbed one photon to be excited from the ground state <sup>1</sup><i>A<sub>g</sub></i>(<i>S</i><sub>0</sub>) to the first excited state <sup>1</sup><i>B</i><sub>2u</sub>(<i>S</i><sub>1</sub>), then absorbed another photon to be ionized. The relationship between the signal intensity of <i>p</i>-dichlorobenzene molecular ion C<sub>6</sub>H<sub>4</sub><sup>35</sup>Cl<sup>+</sup><sub>2</sub> at 248-nm wavelength and the laser power was given. The 1.52 power index of C<sub>6</sub>H<sub>4</sub><sup>35</sup>Cl<sup>+</sup><sub>2</sub> was a typical identification of the 3/2 power law. The relationship between the ion signal intensity of C<sub>6</sub>H<sub>4</sub><sup>35</sup>Cl<sup>+</sup><sub>2</sub> and the sample concentration was close to a linear one in the ppm(V/V) range, which led to a detection limit of 125 ppb(V/V) for <i>p</i>-dichlorobenzene.
© 2008 Chinese Optics Letters
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