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The anharmonic constants of MNH 2 (M = Li, Na, K) at B3P86/6-311++G (3df, 2pd) theoretical level. The change of metal atoms has no significant influence on the tagged anharmonic constants of MNH 2. [Display omitted] • The spectroscopic properties of NaNH 2 are studied by DFT and MP2. • The B3P86/6-311++G (3df, 2pd) results well reproduce the experimental values. • The spectroscopic properties of KNH 2 are predicted at B3P86/6-311++G (3df, 2pd). • The effects of metal atoms on some spectroscopic constants of MNH 2 are intuitively analyzed. The spectroscopic properties and anharmonic force fields of NaNH 2 are studied in present work by DFT (B3P86 and B3PW91) and MP2 methods in combination with 6-311++G(2d, 2p) and 6-311++G(3df, 2pd) basis sets. The calculated equilibrium geometry, ground state rotational constants and centrifugal distortion constants of NaNH 2 at B3P86/6-311++G(3df, 2pd) theoretical level agree very well with the corresponding experimental values. Noteworthy, some spectroscopic constants and anharmonic force fields of NaNH 2 , which have not been experimentally measured, are firstly predicted. In addition, the spectroscopic properties of KNH 2 are also predicted at the B3P86/6-311++G(3df, 2pd) level of theory. The influences of metal atoms on the equilibrium geometry, anharmonic constants, rotational constants, centrifugal distortion constants of MNH 2 (M = Li, Na, K) are analyzed intuitively. One can find that the metal atoms affect the rotational constants, part of centrifugal distortion constants (D K , D JK , H K , and H KJ), M-N bond length and some anharmonic constants of MNH 2. [ABSTRACT FROM AUTHOR]

The equilibrium geometries of c-H 2 C 3 O at B3LYP/aug-cc-pVTZ and HCCCHO and CH 2 CCO at MP2 /aug-cc-pVTZ theoretical level. The three C atoms of c-H 2 C 3 O form a ring, and the three C atoms of the other two isomers form a chain. The difference of structure of three isomers result in the significant difference of spectral properties. [Display omitted] • The relationship between structure and spectral properties of isomers are analyzed. • The ingredients of complex vibration modes of three isomers of C 3 H 2 O are discussed. • The geometries, energies and a series of spectral constants of isomers are predicted. The spectroscopic parameters and anharmonic force fields of three isomers (c-H 2 C 3 O, HCCCHO and CH 2 CCO) of C 3 H 2 O have been calculated by Density Functional Theory (B3LYP, CAM-B3LYP, wB97XD) and second-order Møller-Plesset perturbation theory (MP2) combining with 6–311++G (3df, 3pd) and aug-cc-pVTZ basis sets. The equilibrium geometries, energies, rotational constants, harmonic and fundamental frequencies, and centrifugal distortion constants of three isomers of C 3 H 2 O are calculated and compared with the existed results. The anharmonic constants, vibration–rotation interaction constants, Coriolis coupling constants and force constants of three isomers of C 3 H 2 O are firstly predicted. The ingredients of complex vibration modes, and infrared spectral characteristics of three isomers as well as the relationship between structure and spectroscopic properties are detailedly discussed. [ABSTRACT FROM AUTHOR]

The exploration for the four possible isomers of sulfur trioxide (SO 3) has led to the analysis of spectroscopic constants and anharmonic force fields for cis-OSOO, trans-OSOO, OS(=O) O and SOOO. Quantum chemical calculations are performed with Density Functional Theory (DFT) by employing B3LYP, B3P86 and B3PW91 three different functionals, in combination with Dunning's correlation-consistent cc-pVnZ, aug-cc-pVnZ (n = T, Q) basis sets. The equilibrium geometries, energies, force constants, a series of spectroscopic constants of these four isomers of SO 3 are calculated. The relationship between their structures and spectroscopic properties are analyzed in detail. The present results well reproduce the previous corresponding theoretical or experimental values. Therefore, we hope that our predictions on the isomers of SO 3 can provide the useful reference to further study their spectroscopic properties. Unlabelled Image • All four isomers of SO 3 have stable structures and their energies closely related to their structures. • The equilibrium geometries, energies and a series of spectroscopic constants for four isomers of SO 3 are predicted. • The relationship between the structures of four isomers of SO 3 and spectroscopic properties are analyzed in detail. [ABSTRACT FROM AUTHOR]