177,138 research outputs found
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Theoretical calculation of absorption intensities of C2H and C2D
No full textThe theory of dipole-allowed absorption intensities in triatomic molecules is presented for systems with three close-lying electronic states of doublet multiplicity. Its derivation is within the framework of a recently developed variational method [CARTER, S., HANDY, N. C., PUZZARINI, C., TARRONI, R., and PALMIERI, P., 2000, Molec. Phys., 98,1967]. The method has been applied to the calculation of the infrared absorption spectrum of the C2H radical and its deuterated isotopomer for energies up to 10000 cm(-1) above the ground state, using highly accurate ab initio diabatic potential energy and dipole moment surfaces. The calculated spectra agree very well with those recorded experimentally in a neon matrix [FORNEY, D., JACOX, M. E., and THOMPSON, W. E., 1995, J. molee. Spectrosc., 170, 178] and assignments in the high energy region of the IR spectra are proposed for the first time
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Ab initio prediction of the infrared absorption spectrum of the C2Br radical
No full textThe first three electronic states (1(2)A', 2(2)A', 1(2)A '') of the C2Br radical, correlating at linear geometries with (2)Sigma(+) and (2)Pi states, have been studied ab initio, using Multi Reference Configuration Interaction techniques. The electronic ground state is found to have a bent equilibrium geometry, R-CC = 1.2621 angstrom, R-CBr = 1.7967 angstrom, < CCBr 156.1 degrees, with a very low barrier to linearity. Similarly to the valence isoelectronic radicals C2F and C2Cl, this anomalous behaviour is attributed to a strong three-state non-adiabatic electronic interaction. The Sigma, Pi(1/2), Pi(3/2) vibronic energy levels and their absolute infrared absorption intensities at a temperature of 5K have been calculated for the (CCBr)-C-12-C-12-Br-79 isotopomer, to an upper limit of 2000 cm(-1), using ab initio diabatic potential energy and dipole moment surfaces and a recently developed variational method
Vibronic coupling in the A2Pi and B2Sigma+ electronic states of the NCS radical
No full textThe spin-rovibronic energy levels of the A2Pi and B2Sigma+ electronic states of thiocyanate radical have been calculated variationally, using high-level ab initio coupled diabatic potential energy surfaces. Computations up to J = 7/2 have been performed, obtaining all levels with K ≤ 3, for energies up to 2000 cm−1 above the A(000)2Pi3/2 level. The available experimental data have been critically reviewed in the light of the theoretical findings
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Ab initio prediction of the infrared-absorption spectrum of the C2Cl radical
No full textThe three lowest (1(2)A('), 2(2)A('), and 1(2)A(')) potential-energy surfaces of the C2Cl radical, correlating at linear geometries with (2)Sigma(+) and (2)Pi states, have been studied ab initio using a large basis set and multireference configuration-interaction techniques. The electronic ground state is confirmed to be bent with a very low barrier to linearity, due to the strong nonadiabatic electronic interactions taking place in this system. The rovibronic energy levels of the (CCCl)-C-12-C-12-Cl-35 isotopomer and the absolute absorption intensities at a temperature of 5 K have been calculated, to an upper limit of 2000 cm(-1), using diabatic potential-energy and dipole moment surfaces and a recently developed variational method. The resulting vibronic states arise from a strong mixture of all the three electronic components and their assignments are intrinsically ambiguous. (c) 2005 American Institute of Physics
Ab initio study of vibronic coupling in the ozone radical cation
No full textThe rovibronic levels of the X2A1 and A2B2 electronic states of O3+ have been calculated variationally for the first time, using high-level (ICMRCI/cc-pcV5Z) ab initio diabatic potential energy surfaces which
explicitly consider the non-adiabatic interaction between the two states. Vibronic levels for J = 1/2, 3/2 have been calculated and assigned for energies up to 2000 cm-1 above the ground state, making comparisons with recent results from ZEKE photoelectron experiments of ozone. The procedure has good predictive capabilities and it is used to confirm previous assignments and to tentatively identify some unassigned features in the low energy part of the O3+ spectrum
The potential energy and dipole moment surfaces of HOBr
No full textA theoretical study of the spectroscopy of HOBr and its deuterated isotopomer is presented. Highly accurate ab initio potential energy and dipole moment surfaces have been determined at the multireference configuration interaction level of theory, with large triple-ζ quality basis sets. From the analytic expression of the PES, a quartic anharmonic force field is derived, which, after a little empirical adjustment on the harmonic part, is used to evaluate spectroscopic parameters by means of standard perturbative formulae. Comparisons with experiment and previous computations are made
Heavy atom nitroxyl radicals. I: An ab initio study of the ground and lower electronic excited states of the H(2)As=O free radical.
No full textA series of ab initio calculations have been undertaken to predict the spectroscopic properties of the ground and first two excited states of the recently discovered arsenyl (H(2)AsO) free radical. This 13 valence electron species can be viewed as similar to the formaldehyde radical anion with a ground state electron configuration of cdots, three dots, centered(pi)(2)(n)(2)(pi( *))(1). The arsenyl radical is nonplanar (pyramidal) in the ground state with a 59 degrees out-of-plane angle and a 1.67 A AsO bond length. It has a low-lying n-pi( *)(A (2)A(")) excited state (T(e) approximately 5000 cm(-1)) which has a much larger out-of-plane angle (86 degrees ) and longer AsO bond length (1.81 A). The pi-pi( *)(B (2)A(')) excited state at approximately 20 500 cm(-1) is less pyramidal (out-of-plane angle=70 degrees ) and has a somewhat shorter AsO bond (1.77 A). Similar trends are found for the H(2)PO and H(2)NO free radicals, although the latter has a planar ground state, due to sp(2) hybridization of the N atom, and a very long B state AsO bond length. The geometric variations of the ground and excited states of the H(2)EO (E=N, P, As) radicals, as well as the ground states of the corresponding anions and cations, can be readily rationalized from the Walsh diagram of the anion. The variations in the E-O bond length are a result of changes in both the orbital occupancy and pyramidalization of the molecule. The results of the present work have been employed in the analysis of the B (2)A(')-X (2)A(') electronic band system of the H(2)AsO free radical as reported in the companion paper
Heavy atom nitroxyl radicals. VI. The electronic spectrum of jetcooled H2PO, the prototypical phosphoryl free radical
No full textThe previously unknown electronic spectrum of the H2PO free radical has been identified in the 407–337 nm region using a combination of laser-induced fluorescence and single vibronic level emission spectroscopy. High level ab initio predictions of the properties of the ground and first two excited doublet states were used to identify the spectral region in which to search for the electronic transition and were used to aid in the analysis of the data. The band system is assigned as the B2A−X2A electronic transition which involves promotion of an electron from the π to the π* molecular orbital.
The excited state r0 molecular structure was determined by rotational analysis of high resolution LIF spectra to be r(PO) = 1.6710(2) Å, r(PH) = 1.4280(6) Å, θ(HPO) = 105.68(7)◦, θ(HPH)= 93.3(2)◦, and the out-of-plane angle = 66.8(2)◦. The structural changes on electronic excitation,
which include substantial increases in the PO bond length and out-of-plane angle, are as expected based on molecular orbital theory and our previous studies of the isoelectronic H2AsO, Cl2PS, and F2PS free radicals
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