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Imaging HNCO Photodissociation at 201 nm: State-to-State Correlations between CO (\begin{document}$X^1{\Sigma}^+$\end{document} ) and NH (\begin{document}${a}^1{\Delta}$\end{document} ) 下载免费PDF全文
Zhi-guo Zhang Min Xin Yan-ning Wu Shu-tao Zhao Yi-jia Tang Yang Chen 《化学物理学报(中文版)》2018,31(6):735-740
The NH(\begin{document}$a^1$\end{document} \begin{document}$\Delta$\end{document} )+CO(\begin{document}$X^1$\end{document} \begin{document}$\Sigma^+$\end{document} ) product channel for the photodissociation of isocyanic acid (HNCO) on the first excited singlet state S\begin{document}$_1$\end{document} has been investigated by means of time-sliced ion velocity map imaging technique at photolysis wavelengths around 201 nm. The CO product was detected through (2+1) resonance enhanced multiphoton ionization (REMPI). Images were obtained for CO products formed in the ground and vibrational excited state (\begin{document}$v$\end{document} =0 and \begin{document}$v$\end{document} =1). The energy distributions and product angular distributions were obtained from the CO velocity imaging. The correlated NH(\begin{document}$a^1\Delta$\end{document} ) rovibrational state distributions were determined. The vibrational branching ratio of \begin{document}$^1$\end{document} NH (\begin{document}$v$\end{document} =1/\begin{document}$v$\end{document} =0) increases as the rotational state of CO(\begin{document}$v$\end{document} =0) increases initially and decreases afterwards, which indicates a special state-to-state correlation between the \begin{document}$.1$\end{document} NH and CO products. About half of the available energy was partitioned into the translational degree of freedom. The negative anisotropy parameter \begin{document}$\beta$\end{document} indicates that it is a vertical direct dissociation process. 相似文献
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利用从头算RHF/3-21G方法研究了HNCO二聚后生成HNCNH和CO2的反应机理。计算表明,该反应是分步反应,由反应物经第一过渡态生成四元环中间体,再经过第二过渡态分解为产物,与实验得到的结论一致。反应的第一步是速度控制步骤,计算得到的活化位垒为172.55kJ·mol^-1,与实验上测得的176.40±16.30kJ·mol^-1相吻合。反应的第二位垒为83.68kJ·mol^-1,在实验条 相似文献
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本文通过时间切片离子速度成像技术在201 nm附近研究了HNCO分子在S1电子激发态的光解动力学. CO产物通过共振增强多光子电离的方法进行了选态探测,获得了CO产物的振动基态和激发态切片影像. 从CO的影像得到了解离产物的能量分布和空间角分布,确定了NH(a1Δ)产物的振转态分布信息. 研究发现1NH的振动分支比(v=1/v=0)随CO(v=0)转动能的增大先增大后下降,展现了1NH与CO之间特殊的态态相关性. 大约一半的可资用能分配给解离产物的平动自由度. 负的各向异性参数表明HNCO的光解是个快速的直接解离过程. 相似文献
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HNCO与CX(X=F,Cl,Br)自由基反应机理的密度泛函理论研究 总被引:7,自引:0,他引:7
用量子化学密度泛函理论的B3LYP方法,在6-31+G~*水平上按BERNY能量梯度解 析全参数优化了HNCO与CX(X=F,Cl,Br)反应势能面上各驻点的几何构型,通过 振动频率分析确认了中间体和过渡态,内禀反应坐标(IRC)对反应物、中间体、 过渡态和产物的相关性予以证实,对各驻点进行了零点能校正(ZPE)在此基础上 计算了反应能垒。研究结果表明,与HNCO和其它小分子自由基反应不同,HNCO与 CX自由基反应首先发生分子间H原子迁移,随后N与CX的C(1)原子相互靠近成键并 生成较稳定的中间体,再发生N-C(2)键的断裂,完成N向C(1)上的迁移并进一 步解离为产物。反应按反应物→TS1→IM→TS2→产物通道进行。反应为放热反应。 相似文献
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Well-resolved and unambiguous through-bond correlations and NOE data are crucial for high-quality protein structure determination by NMR. In this context, we present here (4, 3)D reduced dimensionality (RD) experiments: H(CC)CONH TOCSY and NOESY HNCO--which instead of (15)N shifts exploit the linear combination of (15)N(i) and (13)C'(i-1) shifts (where i is a residue number) to resolve the through-bond (1)H-(1)H correlations and through-space (1)H-(1)H NOEs. The strategy makes use of the fact that (15)N and (13)C' chemical shifts when combined linearly provide a dispersion which is better compared to those of the individual chemical shifts. The extended dispersion thus available in these experiments will help to obtain the unambiguous side chain and accurate NOE assignments especially for medium-sized alpha-helical or partially unstructured proteins [molecular weight (MW) between 12-15 kDa] as well as higher MW (between 15-25 kDa) folded proteins where spectral overlap renders inaccurate and ambiguous NOEs. Further, these reduced dimensionality experiments in combination with routinely used (15)N and (13)C' edited TOCSY and NOESY experiments will provide an alternative way for high-quality NMR structure determination of large unstable proteins (with very high shift degeneracy), which are not at all amenable to 4D NMR. The utility of these experiments has been demonstrated here using (13)C/(15)N labeled ubiquitin (76 aa) protein. 相似文献
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Chen J Nietlispach D Shaka AJ Mandelshtam VA 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,169(2):215-224
The advantage of the filter diagonalization method (FDM) for analysis of triple-resonance NMR experiments is demonstrated by application to a 3D constant time (CT) HNCO experiment. With a 15N-,13C-labeled human ubiquitin sample (1.0 mM), high spectral resolution was obtained at 500 MHz in 25 min with only 6-8 increments in each of the CT dimensions. This data set size is about a factor of 50-100 smaller than typically required, yet FDM analysis results in a fully resolved spectrum with a sharp peak for each HNCO resonance. Unlike Fourier transform (FT) processing, in which spectral resolution in each dimension is inversely proportional to the acquisition time in this dimension, FDM is a true multi-dimensional method; the resolution in all dimensions is determined by the total information content of the entire signal. As the CT dimensions of the 3D HNCO signal have approximate time-reversal symmetry, they can each be doubled by combining the usual four hyper-complex data sets. This apparent quadrupling of the data is important to the success of the method. Thus, whenever raw sensitivity is not limiting, well-resolved n-dimensional spectra can now be obtained in a small fraction of the usual time. Alternatively, to maximize sensitivity, evolution periods of faster relaxing nuclei may be radically shortened, the total required resolution being obtained through chemical shift encoding of other, more slowly relaxing, spins. Improvements similar to those illustrated with a 3D HNCO spectrum are expected for other triple-resonance spectra, where CT evolution in the indirect dimensions is implemented. 相似文献
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Kaifeng Hu Michaeleen Doucleff G. Marius Clore 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,200(2):173-177
We present a new version of the 3D TROSY HNCO pulse scheme, referred to as HR-TROSY HNCO, with comparable resolution in the 15N dimension to a 2D 1H–15N HSQC experiment. In the conventional 3D TROSY HNCO, the constant time period (1/2JNC 32 ms) severely limits the maximum resolution in the 15N dimension. In the HR-TROSY HNCO experiment presented here, both constant time periods (32 ms each) for coherence forward and backward transfer between 15N and 13C′ are utilized to double the 15N evolution time. This leads to a dramatic enhancement in peak separation along the 15N dimension, making the HR-TROSY HNCO an ideal pulse scheme for accurate paramagnetic relaxation enhancement and residual dipolar coupling measurements. 相似文献
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