Active vibrations of 1-cyanonaphthalene cation studied by mass-analyzed threshold ionization spectroscopy

Cation Vibrations of 1-Methylnaphthalene and 2-Methylnaphthalene through Mass-Analyzed Threshold Ionization Spectroscopy

“…Consequently, the molecular geometry and vibrational coordinates of 1MN in the cationic ground state D 0 must resemble those of the neutral species in the electronically excited state S 1 . Similar findings have been reported for naphthalene, 3 1-fluoronaphthalene, 31 2-fluoronaphthalene, 31 1cyanonaphthalene, 32 1-methoxynaphthalene, 33 and tetracene. 56 As listed in Table 2, the MATI bands shifted from the 0 + band by 434, 495, 549, 690, 768, 849, 969, and 1024 cm −1 result from the in-plane ring deformation vibrations 37 1 , 35 1 , 34 1 , 33 1 , 32 1 , 31 1 , 30 1 , and 29 1 of the 1MN cation in D 0 .…”

“…Table lists the vibronic bands observed in Figure a and their possible assignments. Spectral assignment was performed by comparing the present experimental data with available naphthalene derivative data elsewhere ,,,− and the results predicted from the CIS and TD-B3PW91 calculations by using the 6-311++G­(d,p) basis set. The numbering system of the normal vibrations of 1MN follows Mulliken’s convention .…”

“…The characteristic band 33 1 0 [8 1 0 ] of 1MN corresponds to in-plane ring deformation vibration similar to the breathing motion of benzene derivatives . The vibronic transitions [8̅ 1 0 ], [9 1 0 ], and [8 1 0 ] were, respectively, observed at 436, 501, and 700 cm –1 for naphthalene; 410, 498, and 699 cm –1 for 1-fluoronaphthalene; 448, 507, and 659 cm –1 for 1-cyanonaphthalene; and 448, 507, and 659 cm –1 for trans -1-methoxynaphthalene. ,− This indicates that the nature of a substituent can affect the frequency of each normal vibration. The newly observed bands at 261, 678, 765, 935, and 1088 cm –1 correspond to vibronic transitions 38 1 0 , 48 1 0 , 32 1 0 , 30 1 0 , and 25 1 0 , respectively.…”

“…This indicates that the interaction between the CH 3 and ring of naphthalene is slightly stronger in S 1 than in S 0 . The D 0 ← S 1 transitions of naphthalene derivatives involve the removal of one electron from the aromatic ring. − A methyl group of 1MN and 2MN has an electron-donating nature, which affects the electron density around the conjugative aromatic ring of naphthalene. Consequently, the IEs of 1MN and 2MN were lower than that of naphthalene by 1489 and 1364 cm –1 , respectively.…”

“…Detailed analysis of these spectra yielded information about the active vibrations of the molecules in the electronically excited state S 1 and cationic ground state D 0 in addition to E 1 and the adiabatic IE. Comparing the collected data of 1MN and 2MN with those of naphthalene and naphthalene derivatives ,,,− provided insight into the methyl substitution effect on the transition energy and molecular vibration.…”