Vibrational, Rotational, and Electronic Spectroscopy for Possible Interstellar Detection of AlNH2 and HAlNH
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Abstract We obtained accurate vibrational frequencies, rotational constants, and vertical transition energy for AlNH 2 (X 1 A 1 ) and HAlNH(X 1 A′) isomers using ab initio calculations at various levels of theory. These two isomers are potential candidates for astronomical observation. AlNH 2 and HAlNH are thermodynamically stable, with Al-NH 2 and HAl-NH bond dissociation energies predicted to be 4.39 and 3.60 eV, respectively. The two isomers are characterized by sizable dipole moments of 1.211 and 3.64 D, respectively. The anharmonic frequencies and spectroscopic constants reported for the two isomers should facilitate their experimental differentiation. In addition, we evaluated the evolution of the low-lying electronic states along the stretching coordinates, as well as the absorption cross sections. AlNH 2 absorbs strongly around 287, 249, and 200 nm, whereas the HAlNH absorption is centered around 370 and 233 nm.Keywords:
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This study has been carried out of calculating potential energy curves (Deng-Fan potential and Morse potential) of ground state and dissociation energies of diatomic molecule (AlBr, AlI). Potential energy curves and dissociation energies depended on spectroscopic Parameters (?e, ?exe, re, ?, µ, ?,).
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The coupled-cluster single-double (CCSD) theory in combination with the quadruple correlation-consistent basis set (cc-pVQZ) of Dunning and co-workers is employed to estimate the equilibrium geometry, dissociation energy and vibrational frequencies of the SeN2 radical. The computational results show that the ground state of SeN2 has C2v symmetry and its ground electronic state is X1A1. The equilibrium parameters of the structure are RSe-N=0.1691 nm, RN-N=0.1970 nm, αN-Se-N =71.289°, and the dissociation energy is De=4.78 eV. The vibrational frequencies are ν1=326.9288 cm-1, ν2=808.0161 cm-1, and ν3=948.3430 cm-1, respectively. The whole potential curves for the ground electronic states of SeN and N2 are further scanned using the above method, the potential energy functions and relevant spectroscopic constants are then obtained by least square fitting to the Murrell-Sorbie function. Compared with other theoretical results and the experimental values, our computational results are very accurate. Then the analytic potential energy function of SeN2 is derived by many-body expansion theory. The potential curves correctly describe the configurations and the dissociation energy for the SeN2 radical.
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The potential-energy curve of the lowest 1Σu+ state of He2 is computed in a valence bond scheme using a 17-term wavefunction of Slater orbitals. A maximum in the potential curve occurs at 5.22 a0 with a computed height of 0.153 eV. A rigorous upper bound of 0.364 eV is found for the potential maximum. The rationalized dissociation energy for the best wavefunction is 1.719 eV at Re=2.11 a0, and a rigorous lower bound on the dissociation energy is 1.508 eV.
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The energy,equilibrium geometry and harmonic frequency of the ground state of NaH molecule have been calculated using the quadratic configuration interaction(QCISD) method with the basis set 6-311G(3df,3pd).The potential curve for this molecule have a least square fitted to Murrell-Sorbie function.The spectroscopy constants(B_e,α_e,ω_e,and ω_eχ_e) are calculated,which are in good agreement with the experimental data.B3LYP method are used to optimized the ground-state structure of Na_2H.The results show that the ground state of Na_2H is of C_(2v) symmetry and of X()~2A_1 state,the equilibrium bond length R_(Na-H) equals 0.20635?nm,the bond angle ∠NaHNa equals 95.1028°,the dissociation energy D_e equals 0.650969?eV and the harmonic frequencies are v_1(a_1)=149.7684 cm~(-1),v_2(b_2)=7224602 cm~(-1),v_3(a_2)=7887.3346 cm~(-1).The potential energy function of Na_2H(_(C2v),X()~2A_1) is derived from the many-body expansion theory.The potential energy function describes correctly the configuration and the dissociation energy.
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A general relation between potential energy and internuclear distance is proposed which is applicable to the ground states of diatomic and polyatomic molecules. The relation has the form V = De[1—exp(—nΔr2/2r)]×[1+af(r)], where the parameter n is defined by the equation n = kere/De. For large values of r, the f(r) term assumes the form of a Lennard-Jones (6—12) repulsive potential. With a = 0 the function assumes a simple form which is numerically easier to use and much more accurate than the Morse function. By using the simple function dissociation energies are readily calculated with greater accuracy than hitherto possible through the use of bond lengths, force constants, and anharmonicity constants. Independent empirical methods are given for evaluating the parameter n and with its use anharmonicity constants as well as dissociation energies may be calculated more accurately than was possible previously. The use of the general relation gives improved correlations and predictions of the five spectroscopic constants re, ke, De, ωeχe, and αe. The wide application of these potential functions to a large number of molecules indicates that the potential energy curves for most molecules have a general form to which the proposed relation is a reasonable approximation. The application of the proposed functions to strongly ionic or charged molecules has not been fully investigated.
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Polyatomic ion
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Abstract It is well known that the anharmonic part of the molecular potential function contributes to the vibration-rotation energy and to the apparent molecular geometry, although the anharmonic effect is not so profound as that from its harmonic counterpart. Nevertheless, it cannot simply be ignored for the precise treatment of molecular dynamics and structures. For a better understanding of the molecular potential function, it is highly desirable to extend the force constant calculation to evaluate the terms beyond quadratic, which will give a more realistic potential map of polyatomic molecules for wider ranges of atomic displacements. The vibrational anharmonicity also affects the transition intensities through the mixing vibration-rotation wave functions.
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