The electronic structure of melamine

Abstract

The Pariser-Pam a.s.m.0. treatment has been applied to melamine. The observed spectrum of melamine agrees with that predicted for s-triaminotriazine but not with that predicted for s-tri-iminohexahydrotriazine. The application of the Pariser-Parr treatment to compounds containing amino nitrogen is considered in detail. Various integrals required in the treatment are evaluated, and the choice of suitable initial m.0.s is discussed. Simple Huckel m.0.s proved unsatisfactory, presumably because they overestimate charge transfer. Good results were obtained with m.0.s calculated for an analogous hydrocarbon obtained by replacing each pyridine-type nitrogen by carbon, and each amino nitrogen by a vinyl group. The coefficients of each pair :f a.0.s in a vinyl group are then combined to give a single coefficient of the nitrogen a.0. 10 26 1 * The atomic integrals (pplpp) here involved can be obtained in another empirical way independent of W, and A, (L. Paoloni, unpublished results).

Excited-State Dynamics of Melamine and Its Lysine Derivative Investigated by Femtosecond Transient Absorption Spectroscopy

“…This shoulder was assigned by Hirt and Salley to a 1 ππ* transition, a transition that is symmetry-forbidden in melamine (D 3h point group, neglecting the amino protons) [ 18 ]. Dewar and Paoloni argued that absorption at 240 nm is due to an electronically forbidden, but vibrationally allowed, 1 ππ* transition and a 1 nπ* transition located at approximately the same energy [ 19 ]. The extinction coefficient ( ε ) at 240 nm is approximately 1400 M −1 ·cm −1 , according to our measured absorbance.…”

“…A 1 nπ* state transition is calculated to have a reasonable oscillator strength, and is proposed to contribute to the 240 nm shoulder seen in Figure 2 b. However, experimental evidence suggests that a 1 ππ* transition also contributes to this feature [ 19 ]. Overall, our preliminary calculations support a picture of overlapping and weakly allowed 1 ππ* and 1 nπ* transitions.…”

SCFCI and SCF open‐shell studies of the base components of the nucleic acids

“…For the carbon-heteroatom bond we have used the same method as Miller, Lykos and Schmeising [lo] did for the nitrogen heterocycles; Pwv is determined by the same formula (9) where b is taken to be 5.007 in all cases, and B is taken in such a way that the value chosen for j 3, , , for a definite heteroatom at the corresponding carbon-heteroatom bond length will fit the curve j3(r). The basic j3 values necessary to find B were taken as follows: for the C-N(azo) bond j3 = -2.576 [ l l ] (in this case interpolation by (9) leads to a value close to the one proposed by Dewar and Paolloni [12] for melamine); for the C-N(amino) bond j 3 = -2.35 eV [12] (a close value j3 = -2.39 eV has been used in [13]); for the carbonyl bond C=O, j3 = -3.00 eV [14] which is slightly different from the value in [ 131.…”

“…The total wave functions for the excited states have been expressed as linear combinations of the singlet or triplet singly excited configurations where the summation i runs only over occupied and k over unoccupied orbitals. The expansion coefficients X z + k , p were determined as the components of the eigenvectors of the Hermitian matrix H with the matrix elements m P.V'l (12)…”

Luminescence enhancement by energy transfer in melamine-Y2O3:Tb3+ nanohybrids

“…At the present, we do not have knowledge of melamine excitation spectra to compare with our results, but several works on the absorption of melamine in solution were already published. [23][24][25] According to Dewar and Paolini, 23 the main absorption band of melamine in solution of water and ethanol is dominated by a singlet-singlet transition around 240 nm with a weak shoulder at 313 nm attributed to a singlet-triplet excitation. Most recently, fluorescence excitation spectra of melamine in water show the main excitation peak at 254 nm, with a weak contribution in the region between 260 and 320 nm.…”