三线态二苯基卡宾的动力学稳定效应

通过对二苯基重氮甲烷进行光照射产生了一系列于邻位和对位具有不同大小取代基的三线态二苯基卡宾.用紫外可见光谱对其进行了直接观察,并利用激光闪光光解法测定了三线态二苯基卡宾在室温脱氧苯溶液中的寿命,由此表明在邻位和对位里引入庞大的取代基对三线态二苯基卡宾具有更好的稳定效应.     

立体拥挤二苯基卡宾分子结构的电子效应

通过对二苯基重氮甲烷的光照射产生了一系列具有对称对位取代基的三线态二(2,6-二甲苯基)卡宾.用电子顺磁共振波谱对其进行了研究.通过对不同粘度的基质(matrix)中零磁场分裂参数D和E的测定,依据电子自旋离域取代基常数σr对三线态二苯基卡宾的分子结构的取代基效应进行了分析.并通过对卡宾的热消失温度及其室温脱气苯溶液中寿命的测定,对三线态二(2,6-二甲苯基)卡宾的稳定性进行了定量考察.结果表明,对卡宾中心的自旋电子具有离域效应的取代基使三线态二(2,6-二甲苯基)卡宾采取低能稳定的直线型结构,且显示了更好的热稳定性和更长的寿命.     

卡宾与2-丁烯环加成反应机理的MNDO法研究

用MNDO法研究单线态和三线态卡宾与乙烯,顺式及反式-2-丁烯的反应途径。合理地解释了顺式和反式-2-丁烯与三线态卡宾都形成顺式和反式-2-二甲基环丙烷。用MNDOCI计算了有关反应的反应活化能。     

亚烷基卡宾与亚烷基锂氟类卡宾化学键结构的量子拓扑研究

用ab initio(3-21G)方法对亚烷基卡宾H_2C—C的单线态及三线态结构进行了电子密度拓扑分析,说明了它们的亲电、亲核反应方向,讨论了亚烷基锂氟类卡宾H_2C—CLiF的4种构型,论证了该分子中不存在四元环结构、Li—C键以静电作用为主的特性,并预测了加成反应机理。     

二（2,6-二甲基-4-甲氧基）苯基卡宾的产生和反应

为了考察卡宾稳定性的电子效应,合成了对位具有强推电性甲氧基的二（2, 6-二甲基-4-甲氧基）苯基重氮甲烷(1c),通过光分解而产生了二（2,6-二甲基- 4-甲氧基）苯基卡宾(2c)。分别用电子顺磁共振（EPR）光谱,紫外可见(UV/vis) 光谱及激光闪光光分解法对二（2,6-二甲基-4-甲氧基）苯基卡宾(2c)的产生和衰 减过程进行了详细的观察。由于甲氧基的强推电子作用使二苯基卡宾的稳定性大大 降低,其二次动力学衰减速度常数为130s~(-1),是对位非取代二苯基卡宾(2b) (14s~(-1))的约9倍,且室温苯溶液中的寿命为20ms,仅为2b(180ms)的1/9。且通过 产物分析对二（2,6-二甲基-4-甲氧基）苯基卡宾(2c)的反应及甲氧基的取代基效 应进行了详细探讨。     

分子形貌所指示的羟基卡宾及其衍生物的质子转移反应

分子形貌(Molecular face, MF)定义分子的内禀电子转折边界面,同时在其上计算并描绘出前沿电子密度(MFED). MF不仅能显示分子的形状和大小,还能够指示分子的化学反应性.应用M06-2X/6-311++G(d,p)理论方法,对单线态和三线态羟基卡宾分子及其衍生物的质子化反应进行研究并计算了这些反应的活化能.结果表明,吸电性和供电性较强的取代基,均使单线态反应活化能增大,只有吸电性较强的─CN才能使三线态反应活化能增大.应用分子形貌理论研究了上述反应,不仅展示出分子的形貌变化、与反应位点的关联,以及有关物理量的变化倾向,而且还定量地显示出,单线态羟基卡宾及其衍生物分子边界面上前沿电子密度极大值与极小值的差值,与其质子转移反应的活化能之间存在线性相关.     

单态卡宾与臭氧反应机理的量子化学研究

为了研究单态卡宾与臭氧反应机理,本文采用密度泛函理论Gaussian-3方法(G3B3)优化了反应物、中间体、过渡态和产物的几何构型。探讨了单态卡宾与臭氧反应可能途径,并通过频率分析对过渡态和中间体进行了验证,研究结果表明：单态卡宾与臭氧反应有两条反应通道,分别具有亲核反应和亲电反应特征,相对而言亲核反应通道较易发生,且为强放热反应。     

微波辐射法合成喹喔啉铱（Ⅲ）配合物及其发光性质

采用微波辐射加热方法,将2,3-二苯基喹喔啉（DPQ）与水合三氯化铱（IrCl3•H2O）反应,合成了一种新型三环喹喔啉铱配合物[Ir(DPQ)3],通过元素分析,1H NMR和质谱方法对配合物结构进行了表征,并初步研究了配合物的吸收光谱和荧光光谱。结果表明,配合物Ir(DPQ)3在387和458nm处存在单线态1MLCT（金属到配体的电荷跃迁）和三线态3MLCT的吸收;在634nm 处有较强的金属配合物三线态的磷光发射。     

卟吩内酯化学:区域异构效应及其在稀土化学生物学中的应用

卟啉的区域异构效应对其电子结构和生物功能产生重要影响,β位羰基取代的不饱和卟啉衍生物尤为明显.在卟吩内酯化合物中,通过引入二内酯结构和控制内酯基团的取向精准调控卟啉配体的三线态能级,实现了对Yb3+近红外发光、单线态氧敏化、光催化反应和三线态湮灭上转换等三线态能量传递过程的调控.通过芳香性的调控实现了对区域异构效应的放...     

CH3N3的光解-生成三线态CH3N自由基的光谱证据

研究了ＣＨ３Ｎ３有第一电子吸收带的光解，获得了生成三线态ＣＨ３Ｎ自由基的重要证据并对可能的反应机制进行了讨论，其机理以激发态ＣＨ３Ｎ３经单线态三线态相互作用后解离生成三线态自由基的可能性较大。     

CH radical production from 248 nm photolysis or discharge-jet dissociation of CHBr3 probed by cavity ring-down absorption spectroscopy

The A-X bands of the CH radical, produced in a 248 nm two-photon photolysis or in a supersonic jet discharge of CHBr(3), have been observed via cavity ring-down absorption spectroscopy. Bromoform is a well-known photolytic source of CH radicals, though no quantitative measurement of the CH production efficiency has yet been reported. The aim of the present work is to quantify the CH production from both photolysis and discharge of CHBr(3). In the case of photolysis, the range of pressure and laser fluences was carefully chosen to avoid postphotolysis reactions with the highly reactive CH radical. The CH production efficiency at 248 nm has been measured to be Phi=N(CH)N(CHBr(3))=(5.0+/-2.5)10(-4) for a photolysis laser fluence of 44 mJ cm(-2) per pulse corresponding to a two-photon process only. In addition, the internal energy distribution of CH(X (2)Pi) has been obtained, and thermalized population distributions have been simulated, leading to an average vibrational temperature T(vib)=1800+/-50 K and a rotational temperature T(rot)=300+/-20 K. An alternative technique for producing the CH radical has been tested using discharge-induced dissociation of CHBr(3) in a supersonic expansion. The CH product was analyzed using the same cavity ring-down spectroscopy setup. The production of CH by discharge appears to be as efficient as the photolysis technique and leads to rotationally relaxed radicals.     

Deprotonation of short-living radical cations of pyrrolylbenzenes*

The deprotonation reaction of radical cations of 1-(2-pyrrolyl)-4-(1-vinyl-2-pyrrolyl)benzene has been studied by nanosecond laser photolysis. Bimolecular rate constants have been determined for the transfer of proton to the heterocyclic base. Analysis of the yields has been carried out of the final products of the radical-cation reaction of 1-(2-pyrrolyl)-4-(1-vinyl-2-pyrrolyl)benzene in the presence and absence of bases. Comparison of the results of impulse and stationary photolysis showed that inhibition of the radical cation reaction occurs at the stage of forming the radical cations.     

Photolysis of methylcobalamin: identification of the relevant excited states involved in Co-C bond scission

The relevant excited states involved in the photolysis of methylcobalamin (MeCbl) have been examined by means of time-dependent density functional theory (TD-DFT). The low-lying singlet and triplet excited states have been calculated along the Co-C bond at the TD-DFT/BP86/6-31g(d) level of theory in order to investigate the dissociation process of MeCbl. These calculations have shown that the photodissociation is mediated by the repulsive 3(sigmaCo-C --> sigma*Co-C) triplet state. The key metastable photoproduct involved in Co-C bond photolysis was identified as an S1 state having predominantly dCo --> pi*corrin metal-ligand charge transfer (MLCT) character.     

Photolysis of 4-oxo-2-pentenal in the 190-460 nm region

We have studied the gas-phase photolysis of 4-oxo-2-pentenal by laser photolysis combined with cavity ring-down spectroscopy. Absorption cross sections of cis- and trans-4-oxo-2-pentenal have been measured in the 190-460 nm region. The product channel following 193, 248, 308, and 351 nm photolysis of 4-oxo-2-pentenal was investigated. The HCO radical is a photodissociation product of 4-oxo-2-pentenal only at 193 and 248 nm. The HCO quantum yields from the photolysis of a mainly trans-4-oxo-2-pentenal sample are 0.13 +/- 0.02 and 0.014 +/- 0.003 at 193 and 248 nm, where errors quoted (1sigma) represent experimental scatter. The HCO quantum yields from the photolysis of a mainly cis-4-oxo-2-pentenal sample are 0.078 +/- 0.012 and 0.018 +/- 0.007 at 193 and 248 nm, where errors quoted (1sigma) represent experimental scatter. The end-products from 193, 248, 308, and 351 nm photolysis of 4-oxo-2-pentenal (the 4-oxo-2-pentenal sample had a tran/cis ratio of 1.062:1) have been determined by FTIR. Ethane, methyl vinyl ketone, and 5-methyl-3H-furan-2-one have been observed, suggesting the occurrence of 4-oxo-2-pentenal photolysis pathways such as CH(3)COCH=CHCHO + hnu --> CH(3) + COCH=CHCHO, CH(3)COCH=CHCHO + hnu --> CH(3)COCH=CH(2) + CO, and CH(3)COCH=CHCHO + hnu --> 5-methyl-3H-furan-2-one. The estimated yields for the CH(3) + COCH=CHCHO channel are about 25%, 33%, 31%, and 23% at 193, 248, 308, and 351 nm, respectively. The absolute uncertainties in the determination of CH(3) + COCH=CHCHO yields are within 55% at 193 nm, and 65% at 248, 308, and 351 nm. The estimated yields for the CH(3)COCH=CH(2) + CO channel are about 25%, 23%, 40%, and 33% at 193, 248, 308, and 351 nm, respectively. The absolute uncertainties in the determination of CH(3)COCH=CH(2) yields are within 80% at 193 and 248 nm and 65% at 308 and 351 nm. The estimated yields for the 5-methyl-3H-furan-2-one channel are about 1.2%, 2.1%, 5.3%, and 5.5% at 193, 248, 308, and 351 nm, respectively. The absolute uncertainties in the determination of 5-methyl-3H-furan-2-one yields are about 23%, 86%, 40%, and 46% at 193, 248, 308, and 351 nm. Results from our investigation indicate that photolysis is a dominant removal pathway for 4-oxo-2-pentenal degradation in the atmosphere.     

Effect of borate buffer on the photolysis of riboflavin in aqueous solution

The photolysis of riboflavin (RF) in the presence of borate buffer (0.1-0.5M) at pH 8.0-10.5 has been studied using a specific multicomponent spectrophotometric method for the determination of RF and photoproducts, formylmethylflavin (FMF), lumichrome (LC) and lumiflavin (LF). The overall first-order rate constants for the photolysis of RF (1.55-4.36 x 10(-2)min(-1)) and the rate constants for the formation of FMF (1.16-3.52 x 10(-2)min(-1)) and LC (0.24-0.84 x 10(-2)min(-1)) have been determined. The values of all these rate constants decrease with an increase in buffer concentration suggesting the inhibition of photolysis reaction by borate species. The kinetic data support the formation of a RF-borate complex involving the ribityl side chain to cause the inhibition of photolysis. The second-order rate constants for the borate inhibited reaction range from 1.17-3.94 x 10(-2)M(-1)min(-1). The log k-pH profiles for the reaction at various buffer concentrations indicate a gradual increase in rate, with pH, up to 10 followed by a decrease in rate at pH 10.5 probably due to ionization of RF and quenching of fluorescence by borate species. A graph of second-order rate constants against pH is a sigmoid curve showing that the rate of photolysis increases with an increase in pH. The results suggest the involvement of excited singlet state, in addition to excited triplet state, in the formation of LC.     

Vector properties of the O(1D2) fragment produced from the photolysis of ozone in the wavelength range of 298 to 320 nm

The speed averaged translational anisotropy and electronic angular momentum polarization of the O(1D2) atomic fragment formed from the photodissociation of ozone in the atmospherically important long wavelength region of the Hartley band (298 to 320 nm) have been measured using resonance enhanced multiphoton ionization time of flight mass spectrometry. The translational anisotropy parameter, beta, is found to decline from 1.1 for photolysis at 300 nm to a minimum value of 0 at 310 nm which is the threshold for production of O(1D2) in conjunction with the O2(a 1Deltag v = 0) molecular cofragment. For photolysis wavelengths greater than 310 nm, O(1D2) is formed from the dissociation of internally excited ozone molecules. The corresponding beta parameters are markedly lower than for atomic fragments produced with the same speed from the photolysis of ground state ozone molecules. This result is consistent with two different pathways contributing to the photolysis of internally excited ozone at the longest wavelengths studied corresponding to initial internal excitation either in the symmetric or asymmetric stretching vibration. In addition, the polarization of the atomic angular momentum has been determined with the incoherent polarization parameters a0(2)(||) and a0(2)(_|) increasing from values of -0.53 and -0.62 at 300 nm to -0.37 and -0.19 at 317 nm, consistent with the increasing contribution from the photolysis of internally excited ozone as the dissociation wavelength lengthens. Evaluation of these alignment parameters allows the populations of the magnetic substrates, mj, to be determined. For example, for a photolysis wavelength of 303 nm the populations of mj = 0, +/- 1, +/- 2 are in the ratio of 0.36: 0.56: 0.08 and this ratio is essentially independent of the photolysis wavelength. The coherent contribution to the atomic polarization is quantified by the Re{a1(2)(||, _|)} and Im{a1(1)(||, _|)} parameters and these are found to vary from -0.21 and 0.21 at 300 nm to -0.04 and 0.24 at 313 nm, respectively.     

Atmospheric chemistry of CHF2CHO: study of the IR and UV-vis absorption cross sections, photolysis, and OH-, Cl-, and NO3-initiated oxidation

The infrared and ultraviolet-visible absorption cross sections, effective quantum yield of photolysis, and OH, Cl, and NO3 reaction rate coefficients of CHF2CHO are reported. Relative rate measurements at 298 +/- 2 K and 1013 +/- 10 hPa gave kOH = (1.8 +/- 0.4) x 10(-12) cm3 molecule(-1) s(-1) (propane as reference compound), kCl = (1.24 +/- 0.13) x 10(-11) cm3 molecule(-1) s(-1) (ethane as reference compound), and kNO3 = (5.9 +/- 1.7) x 10(-17) cm3 molecule(-1) s(-1) (trans-dichloroethene as reference compound). The photolysis of CHF2CHO has been investigated under pseudonatural tropospheric conditions in the European simulation chamber, Valencia, Spain (EUPHORE), and an effective quantum yield of photolysis equal to 0.30 +/- 0.05 over the wavelength range 290-500 nm has been extracted. The tropospheric lifetime of CHF2CHO is estimated to be around 1 day and is determined by photolysis. The observed photolysis rates of CH3CHO, CHF2CHO, and CF3CHO are discussed on the basis of results from quantum chemical calculations.     

Trimethyl acetate on TiO2(110): preparation and anaerobic photolysis

The preparation and anaerobic ultraviolet photolysis of trimethyl acetate (TMA) on rutile TiO(2)(110) have been examined with an emphasis on reaction paths. Substrates for photolysis were prepared by dosing trimethyl acetic acid at 100, 300, and 550 K. The chemistry was characterized by mass spectrometry during dosing and by H(2)O adsorption and temperature programmed desorption (TPD) after dosing. Using TPD after photolysis and mass spectrometry during photolysis, the products ejected and retained during photolysis were sought. The photolysis results are interpreted using the following mechanistic model. Photons with energies exceeding 3 eV create electron-hole pairs in the substrate. With probabilities of 10(-5) or lower, the holes initiate TMA chemistry by extracting an electron from the pi orbital of the carboxylate moiety. The accompanying electrons are trapped at the surface and inhibit subsequent events of this chemistry. The electron-deficient intermediate, TMA, decarboxylates to form CO(2) and either chemisorbed tert-butyl (-C(CH(3))(3)) or physisorbed i-butene. For photolysis at 100 or 200 K, the -C(CH(3))(3) accumulates and there is a slow photon-driven secondary reaction that, with a source of H, hydrogenates adsorbed tert-butyl to physisorbed i-butane. For photolysis at 300 K, -C(CH(3))(3) thermally reacts to form and desorb i-butene and i-butane during photolysis.     

Quantum yields for Cl(2P(j)) atom formation from the photolysis of chlorofluorocarbons and chlorinated hydrocarbons at 193.3 nm

Cl(2P(3/2)) and Cl*(2P(1/2)) atoms produced from the photodissociation of chlorofluorocarbons (CFCs) and chlorinated hydrocarbons at 193.3 nm have been detected quantitatively by a technique of vacuum ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy at 135.2 and 134.7 nm for j = 1/2 and 3/2, respectively. The quantum yields for total Cl-atom formation in the 193.3 nm photolysis at 295 +/- 2 K have been determined to be 1.03 +/- 0.09, 1.01 +/- 0.08, 1.03 +/- 0.08, 1.03 +/- 0.10, 1.41 +/- 0.14, 1.02 +/- 0.08, and 0.98 +/- 0.08 for CF2Cl2, CFCl3, CH2Cl2, CHCl3, CCl4, CHFCl2, and CCl3CF3, respectively. Those results suggest that the single C-Cl bond rupture always occurs in the photolysis of these molecules except for CCl4. Formation of two Cl atoms partly takes place in the photodissociation of CCl4. The quantum yields for total Cl-atom formation in the 193.3 nm photolysis of CHBr2Cl and CHBrClCF3 are 0.27 +/- 0.02 and 0.28 +/- 0.02, respectively, which suggests that the C-Br bond rupture is a main channel in the photodissociation processes. The branching ratios between the spin-orbit states, Cl*(2P(1/2)) and Cl(2P(3/2)), have also been determined for the photodissociation of the chlorinated compounds at 193.3 nm. The UV photodissociation processes giving rise to formation of Cl(2P(j)) atoms from the chlorinated compounds studied here have been discussed.     

Relative tropospheric photolysis rates of HCHO and HCDO measured at the European Photoreactor Facility

The relative photolysis rates of HCHO and HCDO have been studied in May 2004 at the European Photoreactor Facility (EUPHORE) in Valencia, Spain. The photolytic loss of HCDO was measured relative to HCHO by long path FT-IR and DOAS detection during the course of the experiment. The isotopic composition of the reaction product H(2) was determined by isotope ratio mass spectrometry (IRMS) on air samples taken during the photolysis experiments. The relative photolysis rate obtained by FTIR is j(HCHO)/j(HCDO) = 1.58 +/- 0.03. The ratios of the photolysis rates for the molecular and the radical channels obtained from the IRMS data, in combination with the quantum yield of the molecular channel in the photolysis of HCHO, Phi(HCHO-->H(2)+CO) (JPL Publication 06-2), are j(HCHO-->H(2)+CO/jHCDO-->HD+CO) = 1.82 +/- 0.07 and j(HCHO-->H+HCO/(jHCDO-->H+DCO + jHCDO-->D+HCO)) = 1.10 +/- 0.06. The atmospheric implications of the large isotope effect in the relative rate of photolysis and quantum yield of the formaldehyde isotopologues are discussed in relation to the global hydrogen budget.