Substituent effects in the VUV absorption spectra of monochlorobenzene and o-, m-, and p-dichlorobenzene

doi:10.1016/0022-2852(85)90186-9

Journal of Molecular Spectroscopy

Volume 112, Issue 1, July 1985, Pages 8-17

https://doi.org/10.1016/0022-2852(85)90186-9 Get rights and content

Abstract

Gas phase VUV absorption cross sections of chlorobenzene and o-, m-, and p-dichlorobenzene are determined in the energy range from 43 000 to 60 000 cm⁻¹ at 0.3 nm resolution using a gas saturation method. Oscillator strengths for the bands corresponding to transitions to the upper states B̃ ¹B_1u and C̃ ¹E_1u of benzene are determined by integration over the respective band regions. The structures of the spectra and the bathochromic shifts of the chlorinated compounds with respect to the parent molecule, benzene, are discussed and compared to those of spectra in solution.

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However, analysis of the absorption cross-sectional data in the respective spectral range is critical to finding details of the nonlinear effect of temperature on the inversion results of the differential absorption spectra. The absorption cross sections of chlorobenzene have been studied in some detail theoretically and experimentally at room temperature (25 degreesC/298 K) [20,21]. Mackey et al. observed the absorption cross section of chlorobenzene from 260 to 280 nm at six different temperatures in the range 473–973 K[22].
Chlorobenzene is considered an essential organic synthesis intermediate and a precursor for the generation of persistent organic compounds in the waste disposal process, for which accurate detection of gaseous chlorobenzene can further help understand and control various chemical processes and effectively reduce pollution. Differential optical absorption spectroscopy is a reliable online method for detecting gaseous chlorobenzenes. It is crucial to investigate the effect of temperature on the optical absorption of the chlorobenzenes to quantify chlorobenzenes more precisely at various temperatures. A method to fix the effect of temperature variation on absorption spectra of chlorobenzene is initially proposed in this study, and it gave accurate concentrations. The proposed method can effectively improve the accuracy of chlorobenzene concentration measurements with an inverse concentration deviation of 3.2 % or less. The differential absorption cross sections at various temperatures are studied to understand how chlorobenzene absorption cross sections vary with temperature. Such a study is also helpful in reducing the concentration inversion errors induced by the variation of absorption cross sections of chlorobenzene with temperature. A novel method of introducing the binary function of the differential absorption cross sections with respect to wavelength and temperature is also proposed. The fitting of the binary function is done by downscaling functions at fixed wavelength and fixed temperature,respectively. Both fitting approaches obtained continuous differential absorption cross sections in the 201–220 nm wavelength band and 288–473 K temperature range, along with less than 2.74 % deviation in the concentration inversion measurements. Finally, based on the temperature specificity of the shape of the differential absorption cross sections, we developed another method using differential absorption spectroscopy for the simultaneous measurement of temperature and concentration, with a temperature prediction error of less than 1.89 %. This method is favorable to the applications of differential absorption spectroscopy in simultaneous measurement of temperature and concentration.
Vibronic relaxation dynamics of o-dichlorobenzene in its lowest excited singlet state
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Citation Excerpt :
Clearly, the origins of peak e and h are different from that of peak f and g. In order to understand origins of these photoelectrons, the energy diagram of relevant vibrations, excited electronic states of neutral and ionic o-DCB is given in Fig. 3, based upon previous reports [4,7,9,10,37]. The energy of one probe photon is 1.528 eV, which means at least four probe photons must be absorbed for producing photoelectron with kinetic energy of 1.77 eV from the vibrationally excited S1 by 252 nm, according to energy conservation: Ek = hvpump + 4hvprobe − Eion, where Eion is the cation energy.
Vibronic dynamics of o-dichlorobenzene in its lowest excited singlet state, S₁, is investigated in real time by using femtosecond pump-probe method, combined with time-of-flight mass spectroscopy and photoelectron velocity mapping technique. Relaxation processes for the excitation in the range of 276–252 nm can be fitted by single exponential decay model, while in the case of wavelength shorter than 252 nm two-exponential decay model must be adopted for simulating transient profiles. Lifetime constants of the vibrationally excited S₁ states change from 651 ± 10 ps for 276 nm excitation to 61 ± 1 ps for 242 nm excitation. Both the internal conversion from the S₁ to the highly vibrationally excited ground state S₀ and the intersystem crossing from the S₁ to the triplet state are supposed to play important roles in de-excitation processes. Exponential fitting of the de-excitation rates on the excitation energy implies such de-excitation process starts from the highly vibrationally excited S₀ state, which is validated, by probing the relaxation following photoexcitation at 281 nm, below the S₁ origin. Time-dependent photoelectron kinetic energy distributions have been obtained experimentally. As the excitation wavelength changes from 276 nm to 242 nm, different cationic vibronic vibrations can be populated, determined by the Franck-Condon factors between the large geometry distorted excited singlet states and final cationic states.
A quint-wavelength UV spectroscopy for simultaneous determination of dichlorobenzene, chlorobenzene, and benzene in simulated water reduced by nanoscale zero-valent Fe/Ni bimetal
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In order to overcome this weakness, the solid phase microextraction (SPME) based headspace GC method has been introduced [24]. However, the method is not suitable to be used in the quantification of the chlorobenzene compounds at the interested concentration range for the nanoscale zero-valent Fe/Ni bimetal evaluation, because of the poor repeatability in the SPME process [25,26]. Since aromatic compounds have strong absorption in UV wavelength range, these chlorobenzene compounds can be simply determined spectroscopically [27,28].
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The VUV absorption spectrum of phosgene, COCl₂, was measured in the wavelength region between 161 and 220 nm using standard single-beam apparatus. Furthermore, quantum yield measurements were performed at 193 nm employing ArF laser photolysis and FTIR product analysis. Both the absorption cross section and quantum yield data are in reasonable agreement with data in the literature, while the occurrence of a pressure effect on the quantum yield still lacks a detailed explanation.
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Absolute absorption cross sections are determined for the three isomeric trichlorobenzenes in the gas phase in the region from 33 000 to 60 000 cm⁻¹, and relative absorption cross sections of the tetrachlorobenzenes, pentachlorobenzene, and hexachlorobenzene are presented in the region from 40 000 to 60 000 cm⁻¹. Spectra in n-hexane solution are determined for comparison. The spectra in the gas phase are compared to the spectra in solution and to spectra of the analogous fluoro compounds. With respect to band shifts a comparison is made to theoretical considerations (developed for spectra in solution) and a revised set of parameters for gas-phase spectra is derived. Vapor pressures for the tetrachlorobenzenes and for pentachlorobenzene are estimated at room temperature from the observed absorption intensities.
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Substituent effects in the VUV absorption spectra of monochlorobenzene and o-, m-, and p-dichlorobenzene

Abstract

Rev. Mod. Phys.

Rev. Mod. Phys.

J. Chem. Phys.

J. Mol. Phys.

J. Phys. Chem.

J. Phys. Chem.

J. Phys. Chem.

Rev. Roum. Chim.