Anharmonic Calculation of the Structure, Vibrational Frequencies and Intensities of the NH₃···trans-HONO Complex

Abstract

The equilibrium geometry of the NH3···trans-HONO complex and the harmonic vibrational frequencies and intensities are calculated in the MP2/aug-cc-pVTZ approximation with the basis set superposition error taken into account. Effects of anharmonic interactions on spectroscopic parameters are studied by solving vibrational Schrödinger equations in 1-4 dimensions using the variational method. Anharmonic vibrational equations are formulated in the space of normal coordinates of the complex. Detailed analysis is performed for the H-bond stretching vibration and internal vibrations of the trans-HONO isomer in the complex. The intermode anharmonicity and anharmonic coupling between two, three, and four vibrational modes are studied on the basis of correct ab initio potential energy surfaces calculated in the above approximation. The combinations of normal modes of the complex most strongly coupled to one another are examined. The calculated frequencies and intensities of vibrational bands are compared with the experimental data on the NH3···trans-HONO complex in an argon matrix and results of earlier calculations of monomeric HONO. In this calculation the strong resonance between the first excited state of the OH stretching vibration and the doubly excited state of the NOH bending vibration of trans-HONO isomer in the complex is thoroughly studied by solving vibrational equations in two and four dimensions.

Quantum-Mechanical Prediction of the Averaged Structure, Anharmonic Vibrational Frequencies, and Intensities of the H2O···trans-HONO Complex and Comparison with the Experiment

“…The last effect has been observed and explained earlier. 11,21 The small differences between the harmonic and 1D anharmonic frequencies of the ν 2 −ν 5 modes are indicative of insignificant mechanical anharmonicity of these vibrations. In the case of the ν 1 , ν 4 , and ν 5 modes, the 1D anharmonic frequency values are in better agreement with the experimental data 9 than the harmonic frequencies.…”

“…The signs and magnitudes of these effects are similar to those predicted for H 3 N••• trans-HONO. 11 Because the trans-HONO molecule almost retains its planar equilibrium structure upon complexation, the OH torsional vibration can be approximately considered as an out-of-plane motion. Then, the root-mean-square deviation of the H atom of trans-HONO perpendicular to the equilibrium position of the NO 1 H 1 plane equals 0.135 and 0.236 Å in the ground 4D state and in the (0,1,0,0) state, respectively.…”

Изотопные Эффекты В Спектрах Комплексов С Водородной Связью. Экспериментальное И Теоретическое Изучение Спектра ИК Поглощения Комплекса (-=sup=-12-=/Sup=-Ch-=sub=-3-=/Sub=-)-=sub=-2-=/Sub=--=sup=-13-=/Sup=-Co...нf

“…При использовании вариационного метода в таких задачах важно выбрать оптимальный вид колебательных координат. В качестве таких координат можно брать изменения отдельных длин связей и углов [15] или нормальные координаты комплекса [16]. В [2] было показано, что выбор массово-взвешенных нормальных координат в качестве колебательных переменных предпочтителен при изучении изотопных эффектов, так как эффекты изменения масс ядер уже частично отражаются в форме нормальных координат.…”

“…В [2] было показано, что выбор массово-взвешенных нормальных координат в качестве колебательных переменных предпочтителен при изучении изотопных эффектов, так как эффекты изменения масс ядер уже частично отражаются в форме нормальных координат. Детали этого варианта вариационного метода изложены в [16,17]. Для комплекса ( 12 CH 3 ) 13 2 CO .…”

Estimations of FH···X hydrogen bond energies from IR intensities: Iogansen's rule revisited

“…The intensity of proton donor stretching band A increases by about one or two orders of magnitude upon formation of a medium strong hydrogen‐bonded complex. It should be noted that although the overall structure of a vibrational band sometimes can be inextricable being a manifold of hot and combination bands (sometimes referred to as Zundel continuum for water molecules in clusters), 33,35,36 the relative increase of its intensity upon formation of a hydrogen bond can be reliably determined 37,38 . To calibrate the band intensities and associate their increase with the strength of a complex, both intensities of the bands of monomers or characteristic bands of other groups (which are not involved in complexation) can be used.…”