Quadrupole Coupling in some H-bonded Organic Systems by ab initio Lattice Calculations of Electric Field Gradients

Palmer, Michael H.; Blair-Fish, John A.

doi:10.1515/zna-1994-1-223

Cited by 11 publications

(3 citation statements)

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“…5. It is known 1,[27][28][29] that the most stable isomer of melamine can exist in two conformations of C s and C 3V symmetry which have very close energies. Their difference is minor and is not relevant to the dissociation mechanism, so we consider below only one C s form (1a).…”

Section: Processes In Ldi: Internal Conversion Fmentioning

confidence: 99%

“…The optimized geometries of various intermediates of C 3 N 6 H 6 and its dissociation products are respectively presented in Figures S1 and S2 (Supporting Information), and their energies are collected in Table . It is known ,− that the most stable isomer of melamine can exist in two conformations of C s and C 3 v symmetry which have very close energies. Their difference is minor and is not relevant to the dissociation mechanism, so we consider below only one C s form ( 1a ).…”

Section: Potential Energy Surface For Melamine Fragmentationmentioning

confidence: 99%

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The Fragmentation of Melamine: A Study via Electron-Impact Ionization, Laser-Desorption Ionization, Collision-Induced Dissociation, and Density Functional Calculations of Potential Energy Surface

Han

et al. 1998

J. Phys. Chem. B

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We have studied the fragmentation of the melamine (2,4,6-triamino-s-triazine) molecule and its deuterated counterparts via electron impact ionization (EI), laser desorption ionization (LDI), and collision-induced dissociation (CID). Our EI and LDI measurements show that the dissociation of melamine is different from the concerted triple dissociation pathway of s-triazine. In EI experiments, the protonated and parent melamine ion (m/z ) 127 (C 3 N 6 H 7 + ) and 126 (C 3 N 6 H 6 + )) were formed initially with 20 and 70 eV electron bombardment. Other fragment ions, such as m/z ) 43 (CN 2 H 3 + ), 53 (C 2 N 2 H + ), 56 (CN 3 H 2 + ), 68 (C 2 N 3 H 2 + ), 83 (C 2 N 4 H 3 + ), 85 (C 2 N 4 H 5 + ), 99 (C 2 N 5 H 5 + ), 110 (C 3 N 5 H 4 + ), etc., were subsequently formed from the decomposition of metastable melamine ions. This speculation was supported by our additional CID measurements. On the other hand, in the LDI experiments the melamine molecule was pumped to 1 1 A′′ and 2 1 A′ excited electronic states, respectively, with 266 and 193 nm lasers. In view of the same fragment ions (m/z ) 43, 45 (CN 2 H 5 + ), 60 (CN 3 H 6 + ), 85, and 127) resulting from the different excited 1 1 A′′ and 2 1 A′ states, we conclude that the fragmentation of melamine in LDI proceeds via internal conversion to its ground potential energy surface (1 1 A′) prior to dissociation. The decomposition mechanism in the ground electronic state has been investigated using the density functional B3LYP/6-31G* and B3LYP/cc-pVTZ methods. All the molecular ions observed in EI experiments can be produced from major and minor neutral fragments of melamine dissociation. The calculations demonstrate the reaction pathways leading to these fragments and predict the corresponding activation energies. The dissociation mechanism of melamine is shown to be distinct from that of s-triazine, because of the presence of mobile hydrogen atoms in the amino groups.

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Section: Processes In Ldi: Internal Conversion Fmentioning

confidence: 99%

Section: Potential Energy Surface For Melamine Fragmentationmentioning

confidence: 99%

The Fragmentation of Melamine: A Study via Electron-Impact Ionization, Laser-Desorption Ionization, Collision-Induced Dissociation, and Density Functional Calculations of Potential Energy Surface

Han

et al. 1998

J. Phys. Chem. B

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“…They are used as critical indicators of the existing α-helices or β-sheets. A variety of theoretical − and experimental methods have been employed to obtain information about the properties of HBs. The prime tool for this purpose is X-ray crystallography .…”

Section: Introductionmentioning

confidence: 99%

A Study on the Intermolecular Hydrogen Bonds of α-Glycylglycine in Its Actual Crystalline Phase Using ab Initio Calculated ¹⁴N and ²H Nuclear Quadrupole Coupling Constants

Elmi

Hadipour

2005

J. Phys. Chem. A

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alpha-Glycylglycine in its actual crystalline phase is studied by ab initio calculated nuclear quadrupole coupling constants. These physical quantities are computed for 2H and 14N in the hydrogen bonds. The type of hydrogen bond is the N-H...O type. The computations are performed with the RHF and B3LYP methods and 6-31++G** and 6-311++G** basis sets using the Gaussian 98 program. Values of the calculated nuclear quadrupole coupling constants are shown in Tables 1-3. The aim of this work is the study of 2H and 14N quadrupole coupling constants which contribute in the CON2H...O=CN2H type of hydrogen bond. The computed nuclear quadrupole coupling constants of 2H nuclei meet the related experimental values. In addition, the computed chi value of 14N belonging to the -CO-14NH- group agrees well with values obtained experimentally. However, there are some discrepancies between calculated 14N chi values of the N+H3 residue and experiments. Also, the values of these physical parameters are calculated for >C2H2 of alpha-glycylglycine in its crystalline phase. Calculations for these parameters are carried out in a single molecule using X-ray diffraction coordinates, too.

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The Calculation of Electric Field Gradients byab initioMethods, and Their Relationship to Experimental Nuclear Quadrupole Coupling Constants

Palmer

1998

Encyclopedia of Computational Chemistry

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The electric field gradient, a 1‐electron operator, is discussed in relation to electronic structure calculations. For atoms which have spin $> 1/2$ , this property leads to the spectroscopically important effect of nuclear quadrupole coupling. These second rank tensor elements are present in diverse spectral determinations, and yield important information concerning the electron distribution in the molecule under study. The nature of the phenomenon is discussed in relation to both atomic and molecular structure, and the results of many studies in vapour, liquid and solid state investigations are given.

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Quadrupole Coupling in some H-bonded Organic Systems by ab initio Lattice Calculations of Electric Field Gradients

Cited by 11 publications

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The Fragmentation of Melamine: A Study via Electron-Impact Ionization, Laser-Desorption Ionization, Collision-Induced Dissociation, and Density Functional Calculations of Potential Energy Surface

The Fragmentation of Melamine: A Study via Electron-Impact Ionization, Laser-Desorption Ionization, Collision-Induced Dissociation, and Density Functional Calculations of Potential Energy Surface

A Study on the Intermolecular Hydrogen Bonds of α-Glycylglycine in Its Actual Crystalline Phase Using ab Initio Calculated ¹⁴N and ²H Nuclear Quadrupole Coupling Constants

The Calculation of Electric Field Gradients byab initioMethods, and Their Relationship to Experimental Nuclear Quadrupole Coupling Constants

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Quadrupole Coupling in some H-bonded Organic Systems by ab initio Lattice Calculations of Electric Field Gradients

Cited by 11 publications

References 0 publications

The Fragmentation of Melamine: A Study via Electron-Impact Ionization, Laser-Desorption Ionization, Collision-Induced Dissociation, and Density Functional Calculations of Potential Energy Surface

The Fragmentation of Melamine: A Study via Electron-Impact Ionization, Laser-Desorption Ionization, Collision-Induced Dissociation, and Density Functional Calculations of Potential Energy Surface

A Study on the Intermolecular Hydrogen Bonds of α-Glycylglycine in Its Actual Crystalline Phase Using ab Initio Calculated 14N and 2H Nuclear Quadrupole Coupling Constants

The Calculation of Electric Field Gradients byab initioMethods, and Their Relationship to Experimental Nuclear Quadrupole Coupling Constants

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A Study on the Intermolecular Hydrogen Bonds of α-Glycylglycine in Its Actual Crystalline Phase Using ab Initio Calculated ¹⁴N and ²H Nuclear Quadrupole Coupling Constants