Abstract
Methylamine is the simplest alkylamine. It is a typical molecule in the field of surface physicochemistry. The basic properties of the structure and reaction activity of this molecule are essential to understand its role in many chemical reactions. Its energy state and ionic structure, ionization dissociation channel and competition have aroused the interest of astronomical and physicochemical researchers. In order to further understand the mechanism of multiphoton dissociation and ionization of methylamine in this energy region, the photodissociation channels of methylamine are studied based on the measured resonance enhanced multiphoton ionization-time-of-flight mass spectrum (TOFMS), mass-selected excitation spectra of the ionized fragment, and laser power index of each ion in a range of 280-287.5 nm. The multiphoton ionization TOFMS of methylamine molecule is obtained at the excited laser wavelength of 283 nm. After calibration, the weaker ion peaks correspond to the C<sup>+</sup>, CH<sup>+</sup>, CH<sub>2</sub><sup>+</sup>, CH<sub>3</sub><sup>+</sup>, NH<sub>2</sub><sup>+</sup>, NH<sub>3</sub><sup>+</sup>, CN<sup>+</sup>, CH<sub>2</sub>NH<sup>+</sup>(CHNH<sub>2</sub><sup>+</sup>, CH<sub>3</sub>N<sup>+</sup>), CH<sub>3</sub>NH<sub>2</sub><sup>+</sup>; the mass-to-charge ratio of stronger peaks except H<sup>+</sup> ions are 27, 28 and 30, respectively, and the mass-to-charge ratio of 28 and 30 belong to CHNH<sup>+</sup>, CH<sub>2</sub>NH<sub>2</sub><sup>+</sup> after analysis and discussion. Combining with the mass separation excitation spectra of the parent ions, it is concluded that there is a repulsive electronic state in the single photon energy. The main dissociation channel is the resonant photodissociation of the parent molecule in the repulsive state produced by one photoabsorption, followed by the photoionization of the fragment through the (1+1) multiphoton process and the further photodissociation of the ionized fragment.
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