Geometries and Energies of Nitrobenzene Studied by CAS-SCF Calculations

Takezaki, Makoto; Hirota, Noboru; Terazima, Masahide; Sato, Hirofumi; Nakajima, Tohru; Kato, Shigekí

doi:10.1021/jp970937v

Cited by 76 publications

(83 citation statements)

References 34 publications

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“…Similar conclusions have been drawn for nitrobenzene and p-nitroaniline. 14,16 On the other hand, the gas-phase equilibrium geometry of NPe*(S 1 ) is predicted to be planar ( Figure 9B). Moreover, the potential along the torsional coordinate is not as shallow as that for the ground state.…”

Section: Discussionmentioning

confidence: 99%

Excited-State Dynamics of Nitroperylene in Solution: Solvent and Excitation Wavelength Dependence

2008

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The photophysics and excited-state dynamics of nitroperylene (NPe) in solvents of various polarities and viscosities, including a room-temperature ionic liquid, have been investigated by femtosecond-resolved transient absorption spectroscopy. The excited-state absorption spectrum was found to depend substantially on solvent polarity. In the most polar solvents, it is very similar to that of the NPe radical cation generated upon bimolecular quenching by an electron acceptor, denoting a substantial charge-transfer character of the S 1 state. Contrary to smaller nitroaromatic compounds, NPe in the S 1 state does not undergo ultrafast intersystem crossing (ISC) but decays mainly by internal conversion (IC). In nonprotic solvents, IC involves low-frequency modes with large amplitude motion associated with the nitro group and depends on both the solvent viscosity and polarity. It takes place on a 100 ps time scale in acetonitrile, while in cyclohexane, it is slow enough for ISC to become competitive. Moreover, both the fluorescence quantum yield and the excited-state dynamics were found to differ, depending on which side of the S 0 -S 1 absorption band excitation was performed. This dependence is explained by the inhomogeneous nature of the absorption spectrum arising from a distribution of twist angles of the nitro group relative to the aromatic plane. On the other hand, such excitation wavelength effects were not observed in protic solvents, where the excited-state lifetime was found to be substantially shorter than that in nonprotic solvents. This behavior is rationalized in terms of a H-bonding interaction, which limits the torsional disorder of NPe and favors ultrafast nonradiative deactivation of the excited state. Transient absorption measurements performed for comparative purpose with nitropyrene in acetonitrile confirm the occurrence of ultrafast ISC in smaller nitroaromatic compounds.

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Section: Discussionmentioning

confidence: 99%

Excited-State Dynamics of Nitroperylene in Solution: Solvent and Excitation Wavelength Dependence

2008

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“…They also obtained the substitution r s -structure and calculated the height of the barrier hindering internal rotation to be 2.9 ± 0.3 kcal/mol. The calculations of optimized geometries and energies in the ground (S 0 ) and excited electronic states of NB by the multiconfiguration method in complete active space (CAS SCF) demonstrated that the energy gap between S 0 and the nearest excited state (T 1 ) may reach *50-60 kcal/mol [5]. The energy of the triplet T 1 state in solution was deduced to be 58 kcal/mol [6].…”

Section: Literature Data On Spectroscopy Studiesmentioning

confidence: 99%

IR spectra of nitrobenzene and nitrobenzene-15N in the gas phase, ab initio analysis of vibrational spectra and reliable force fields of nitrobenzene and 1,3,5-trinitrobenzene. Investigation of equilibrium geometry and internal rotation in these simplest aromatic nitro compounds with one and three rotors by means of electron diffraction, spectroscopic, and quantum chemistry data

et al. 2015

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The IR spectra of gaseous nitrobenzene (NB) and its 15 N isotopomer have been obtained in the frequency range of 3500-250 cm -1 , and the far-IR spectra of their solutions and the NB neat liquid sample have been recorded in the range of 600-30 cm -1 . A detailed description of the spectra of NB and 1,3,5-trinitrobenzene (sym-TNB) and their isotopomers has been accomplished using the force fields calculated at the MP2(full)/aug-cc-pVTZ and MP2(full)/cc-pVTZ levels. Transferability of the refined scale factors for the calculated force constants obtained by the Pulay technique has been used to provide evidence for validity of both interpreting the NB and sym-TNB spectra and refining the calculated force fields. The direct and inverse spectral problems have been solved by variational technique to determine torsional energy levels and refine the potential function by optimizing the V k coefficients in its Fourier series expansion. The height of the MP2(full) barrier to internal rotation has been reduced from 5.5 to 4.5 kcal/mol due to extension of the used basis set from 6-31(d,p) to aug-cc-pVTZ. The method of joint dynamic structural analysis of the GED, MW, and vibrational spectroscopy, and ab initio data in terms of the PES parameters have been applied to investigation of equilibrium geometry and internal rotation in the nonrigid NB and sym-TNB molecules having one and three coupled internal rotors, respectively. The experimental r e -parameter values of both molecules (C 2v and D 3h point group symmetries) are in agreement with those obtained by ab initio calculations. This paper is dedicated to Professor Magdolna Hargittai on the occasion of her 70th birthday.

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“…The low-lying n,π* levels are due to the presence of nonbonding lone-pair orbitals on the oxygen atoms of the nitro group. It has been suggested that the fast ISC of nitroarenes is caused by strong coupling between the excited singlet and triplet states, both of which show large distortions of the nitro group relative to the geometry of the ground state (Takezaki et al 1998;Takezaki et al 1997b). Nitrobenzene also shows no phosphorescence, due to the short lifetime of the lowest excited triplet state (Takezaki et al 1997a).…”

Section: Nitroarenesmentioning

confidence: 99%

Studies of the laser-induced fluorescence of explosives and explosive compositions.

Hargis¹,

Thorne²,

Phifer³

et al. 2006

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Continuing use of explosives by terrorists throughout the world has led to great interest in explosives detection technology, especially in technologies that have potential for standoff detection. This LDRD was undertaken in order to investigate the possible detection of explosive particulates at safe standoff distances in an attempt to identify vehicles that might contain large vehicle bombs (LVBs). The explosives investigated have included the common homogeneous or molecular explosives, 2,4,6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), cyclonite or hexogen (RDX), octogen (HMX), and the heterogeneous explosive, ammonium nitrate/fuel oil (ANFO), and its components. We have investigated standard excited/dispersed fluorescence, laserexcited prompt and delayed dispersed fluorescence using excitation wavelengths of 266 and 355 nm, the effects of polarization of the laser excitation light, and fluorescence imaging microscopy using 365-and 470-nm excitation. The four nitro-based, homogeneous explosives (TNT, PETN, RDX, and HMX) exhibit virtually no native fluorescence, but do exhibit quenching effects of varying magnitude when adsorbed on fluorescing surfaces. Ammonium nitrate and fuel oil mixtures fluoresce primarily due to the fuel oil, and, in some cases, due to the presence of hydrophobic coatings on ammonium nitrate prill or impurities in the ammonium nitrate itself. Pure ammonium nitrate shows no detectable fluorescence. These results are of scientific interest, but they provide little hope for the use of UV-excited fluorescence as a technique to perform safe standoff detection of adsorbed explosive particulates under real-world conditions with a useful degree of reliability. LDRD Studies of the Laser-Induced Fluorescence of Explosives and Explosive Compositions4

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Geometries and Energies of Nitrobenzene Studied by CAS-SCF Calculations

Cited by 76 publications

References 34 publications

Excited-State Dynamics of Nitroperylene in Solution: Solvent and Excitation Wavelength Dependence

Excited-State Dynamics of Nitroperylene in Solution: Solvent and Excitation Wavelength Dependence

Studies of the laser-induced fluorescence of explosives and explosive compositions.

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