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ABSTRACT: We report the first spectroscopic study of a complex consisting of a rare earth atom in combination with ammonia. Using two-color resonance-enhanced multiphoton ionization (REMPI) spectroscopy, the lowest energy electronic transition of YbNH(3) has been found in the near-infrared. The spectrum arises from a spin-forbidden transition between the (1)A(1) ground electronic state and the lowest (3)E excited electronic state. The transition is metal centered and approximately correlates with the Yb 6s6p (3)P ← 6s(2) (1)S transition. The observation of clear spin-orbit structure in the spectrum confirms the C(3v) symmetry of YbNH(3). Vibrational structure is also observed in the REMPI spectrum, which is dominated by excitation of the Yb-N stretching vibration.
The Journal of chemical physics 02/2012; 136(6):064305. · 3.09 Impact Factor
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ABSTRACT: Electronic spectra of LiNH(3) and its partially and fully deuterated analogues are reported for the first time. The spectra have been recorded in the near-infrared and are consistent with two electronic transitions in close proximity, the Ã(2)E-X(2)A(1) and B(2)A(1)-X(2)A(1) systems. Vibrational structure is seen in both systems, with the Li-N-H bending vibration (ν(6)) dominant in the Ã(2)E-X(2)A(1) system and the Li-N stretch (ν(3)) in the B(2)A(1)-X(2)A(1) system. The prominence of the 6(0)(1) band in the Ã(2)E-X(2)A(1) spectrum is attributed to Herzberg-Teller coupling. The proximity of the B(2)A(1) state, which lies a little more than 200 cm(-1) above the Ã(2)E state, is likely to be the primary contributor to this strong vibronic coupling.
The Journal of chemical physics 03/2011; 134(12):124304. · 3.09 Impact Factor
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ABSTRACT: Li(NH(3))(4) has been proposed as a key entity in lithium-ammonia solutions, but its spectral signature has so far proved impossible to distinguish from other species in these solutions. Here we report the first electronic spectrum of Li(NH(3))(4) in the gas phase, which was recorded using mass-selective depletion spectroscopy. Strong absorption is observed in the near-infrared and the band system is assigned to the A (2)T(2)-X (2)A(1) transition in a nominally tetrahedral complex. However, the vibrational structure is indicative of a substantial Jahn-Teller effect in the excited electronic state. The broad and structured spectrum confirms a recent theoretical prediction that the electronic spectrum of Li(NH(3))(4) will strongly overlap with the spectrum of the solvated electron in lithium-ammonia solutions.
The Journal of chemical physics 04/2010; 132(16):161101. · 3.09 Impact Factor
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ABSTRACT: This work combines high level ab initio calculations with multidimensional Franck-Condon calculations to refine and augment previous assignments of the lower wavenumber region of the A (1)B(2) <-- X (1)A(1) band system of fluorobenzene. The strength of the assignment has been greatly assisted by the use of zero electron kinetic energy spectroscopy in a series of pump-probe experiments where the response of the molecule to selective excitation in specific modes prior to ionization has been studied. The net result of this analysis is the reassignment of 7 of the 12 previously assigned bands in the region below about 1000 cm(-1) using a strategy that aims to trace the origins of excited state normal modes of fluorobenzene to the well-known Wilson modes of benzene by taking full account of the Duschinsky mixing that accompanies electronic excitation. Duschinsky normal mode analyses of the ground and first excited states of fluorobenzene as well as the electronic ground state of fluorobenzene cation have shown that the common use of the benzene Wilson notation to describe normal modes of this prototypical benzene derivative is highly questionable, particularly following electronic excitation and ionization.
The Journal of chemical physics 10/2008; 129(10):104303. · 3.09 Impact Factor
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ABSTRACT: The structural properties of phenylacetylene have been investigated in the S(0)((1)A(1)) neutral ground and S(1)((1)B(2)) and S(2)((1)A(1)) singlet excited states and the D(0)((2)B(1)) cationic state using both rovibronic and multidimensional Franck-Condon simulations from data determined via correlated ab initio methods. Results are compared to experimental and ab initio data reported in the literature. (10,10)-CASSCF and a hybrid CASSCF/SACCI frequency analysis using the cc-pVDZ Dunning basis set have been employed to produce vibronic simulations of REMPI/FES, dispersed fluorescence, TPES and MATI spectra. Calculated rotational constants are used where appropriate to compare to rotationally resolved experimental studies. Whilst the simulations are of generally good quality, it is apparent that the distortion of the ring along the long axis upon electronic excitation is underestimated, resulting in smaller predicted changes in ipso and para CCC bond angles and weaker activities in the 6a and 9a modes compared with experiment. Simulations of one-photon MATI spectra on the other hand, which do not rely on excited state methodologies, compare very well with experiment, suggesting that the neutral and cationic ground state geometries are quite accurate, as are the predicted changes in geometry accompanying ionisation. Simulated rotational and vibrational profiles, as well as other calculated physical data, show good agreement with the numerous experimental and computational studies of phenylacetylene in the literature.
Physical Chemistry Chemical Physics 11/2007; 9(40):5436-45. · 3.57 Impact Factor
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ABSTRACT: The fluorobenzene-ammonia van der Waals complex has been studied using a combination of two-color resonance enhanced multiphoton ionization (REMPI) spectroscopy, counterpoise corrected RICC2 ab initio molecular orbital calculations, and multidimensional Franck-Condon analysis. The experimental REMPI spectrum is characterized by a dominant, blueshifted band origin, and weak activity in intermolecular vibrational modes. RICC2 geometry optimizations and numerical vibrational frequency calculations of the neutral ground and first excited states have been performed on a number of different structural isomers of the complex using basis sets ranging from augmented double-zeta to quadruple-zeta level. Ground state basis set superposition error corrected zero-point binding energies show the in-plane sigma complex, forming a pseudo-six-membered ring connecting the fluorine atom and ortho-hydrogen, to be consistently the most stable of all six conformations considered, at all levels of theory. Comparison of computed zero-point excitation energies for the most stable pi and sigma conformers with fluorobenzene show that the sigma complex is the only conformer predicted to exhibit a spectral blueshift upon electronic excitation. The computed neutral ground and first excited state geometries and frequencies were used to perform multidimensional Franck-Condon simulations of the S(1)-S(0) vibronic spectrum for each of the most stable conformers. These simulations yielded null spectra for transitions involving the most stable of the pi complexes, pi(bridge); a spectrum rich in strong intermolecular vibrational structure for the second of the pi complexes, in complete contrast to the experimental spectrum; and for the sigma complex, a spectrum exhibiting weak intermolecular activity in line with that observed experimentally. This last simulation allowed an almost complete vibrational assignment of the intermolecular structure in the REMPI spectrum. The agreement between computational results and experiment overwhelmingly favors assignment of the spectrum to the in-plane sigma complex.
The Journal of Chemical Physics 05/2007; 126(15):154319. · 3.33 Impact Factor
