Fig. 1. The DUV laser ionization mass spectra of gaseous (A) benzene and (B) aniline by ps-pulsed 177.3 nm laser and the Re-TOFMS. (C) Mass spectra of gaseous aniline ionized by a 355 nm laser.

Fig. 1. A sketch showing the customized reflection time-of-flight mass spectrometer (Re-TOFMS) combined with a deep ultraviolet 177.3 nm laser for photo-ionization and photo-dissociation.

Fig. 1. Mapping profiles of the charge distributions by natural population analysis (NPA) and all bond lengths of neutral and cationic benzene (a/b) and aniline (c/d), respectively. Bond lengths are in Å. Atoms in gray, blue, and pink color represent C, N, and H respectively.

Fig. 2. Hydrogen transfer processes and C-C bond cleavages of cationic benzene in productions of the fragment ions C\begin{document}$ _3 $\end{document}H\begin{document}$ _3 $\end{document}\begin{document}$ ^+ $\end{document}, C\begin{document}$ _4 $\end{document}H\begin{document}$ _4 $\end{document}\begin{document}$ ^{+\cdot} $\end{document}, C\begin{document}$ _4 $\end{document}H\begin{document}$ _3 $\end{document}\begin{document}$ ^+ $\end{document}, C\begin{document}$ _4 $\end{document}H\begin{document}$ _2 $\end{document}\begin{document}$ ^{+\cdot} $\end{document}, and C\begin{document}$ _5 $\end{document}H\begin{document}$ _3 $\end{document}\begin{document}$ ^+ $\end{document}. The energy (in eV) of cationic benzene, reaction intermediates (Is), transition states (TSs), and products (Ps) is the sum of electronic and zero-point energies. The unit of the bond length is in Å.

Fig. 2. Schematic view of dissociation mechanism observed for benzene dissociation at 177.3 nm. Mark *, ^+•, ^‡, and ^• refer to electronically excited species, ionic radicals, vibrationally exerted species, neutral radicals, respectively.

Fig. 3. (a) Potential energy scan of C–H bond cleavage of the cationic benzene in forming fragment ion C₆H₅⁺ (m/z = 77). (b) Potential energy scan of C–H/N–H bond cleavage of the cationic aniline in forming fragment ion C₆H₆N⁺ (m/z = 92). The zero-point vibrational energy is not included in the potential scanning calculations.

Fig. 3. (A) Hydrogen transfer process accompanied with consecutive ring opening and re-closing to form a five-membered ring of aniline cation of ion C\begin{document}$ _5 $\end{document}H\begin{document}$ _6 $\end{document}\begin{document}$ ^{+\cdot} $\end{document}. (B) The proposed hydrogen transfer processes and C-N bond cleavage of cationic aniline in producing the fragment ion C\begin{document}$ _6 $\end{document}H\begin{document}$ _6 $\end{document}\begin{document}$ ^{+\cdot} $\end{document}. The energies (in eV) of cationic aniline, reaction intermediates (Is), transition states (TSs), and products (Ps) are the sum of electronic and zero-point energies. The unit of the bond length is in Å.

Fig. 4. Natural bond orbital (NBO) of donor-acceptor (overlap) interactions between (A) C-C and C-N bonds, (B) N atom and C-C bonds, respectively. LP, BD, and BD\begin{document}$ ^* $\end{document} refer to lone pairs, bonding orbitals, and antibonding orbitals, respectively. The values are the second-order perturbative energies \begin{document}$ E $\end{document}(2) in kcal/mol. A-I1, B-I1, and B-I2 correspond to reaction intermediate I1 (in FIG. 3(A)), I1 (in FIG. 3(B)), and I2 (in FIG. 3(B)), respectively. Mark: the carbon atom number of aniline as an illustration in the upper right.

Fig. 4. The potential energy scan of C–C bond cleavage of the cationic benzene in forming fragment ions C₃H₃⁺ (m/z = 39) and C₅H₃⁺ (m/z = 63). The zero-point vibrational energy is not included in the potential scanning calculations.

Fig. 5. The potential energy scan of C–C bond cleavage of the cationic aniline in forming fragment ion C₅H₆^+• (m/z =66) and CNH^• radical. The zero-point vibrational energy is not included in the potential scanning calculations.

Fig. 6. The potential energy scan of C–N bond cleavage of the cationic aniline in forming fragment ion C₆H₆^+• (m/z = 78) and NH^• radical. The zero-point vibrational energy is not included in the potential scanning calculations.

Fig. 7. Natural bond orbital (NBO) of donor–acceptor (overlap) interactions between (A) C−C and C−N bonds, (B) N atom and C-C/C-H bonds, respectively. LP, BD, and BD^* refer to lone pairs, bonding orbitals, and antibonding orbitals, respectively. The values are the second-order perturbative energies E(2) in kcal/mol. A-I1, B-I1, and B-I2 are corresponding to reaction intermediate I1 (in FIG. 3A), I1 (in FIG. 3B), and I2 (in FIG. 3B), respectively.

Table 1. Ionization Energies (IE, in eV), sum of electronic and zero-point energies (EZPV, in Hartree), bond length (d, in Å), and average bond length (đ, in Å) of benzene and aniline molecules and ions at different calculation levels.

Table 2. Natural bond orbital (NBO) donor–acceptor (overlap) interactions for neutral aniline C₆H₇N.

Table 3. Natural bond orbital (NBO) donor–acceptor (overlap) interactions for cationic aniline C₆H₇N^+•.

Table 4. Natural bond orbital (NBO) donor–acceptor (overlap) interactions for A-I1/B-I2 intermediate.

Table 5. Natural bond orbital (NBO) donor–acceptor (overlap) interactions for B-I1 intermediate.