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High accuracy extrapolated ab initio thermochemistry (HEAT) scheme is used for studying the standard heat of formation of vinyl chloride. The enthalpies of the reactions [C.sub.2][H.sub.4] + [Cl.sub.2] -> C[H.sub.2]CHCl + HCl and [C.sub.2][H.sub.2] + HCl -> C[H.sub.2]CHCl are obtained.

Thephotophysics of chromophores is strongly influenced by theirenvironment. Solvation, charge state, and adduct formation significantlyaffect ground and excited state energetics and dynamics. The presentstudy reports on fluorescence emission of rhodamine B cations (RhBH+) and derivatives in the gas phase. Substitution of the acidicproton of RhBH+by alkali metal cations, M+,ranging from lithium to cesium leads to significant and systematicblue shifts of the emission. The gas-phase structures and singlettransition energies of RhBH+and RhBM+, M =Li, Na, K, Rb, and Cs, were investigated using Hartree–Focktheory, density functional methods, second-order Møller–Plessetperturbation theory, and the second-order approximate coupled-clustermodel CC2. Comparison of experimental and theoretical results highlightsthe need for improved quantum chemical methods, while the hypsochromicshift observed upon substitution appears best explained by the Starkeffect due to the inhomogeneous electric field generated by the alkaliions. [ABSTRACT FROM AUTHOR]

We present gas-phase dispersed photoluminescencespectra of europium(III) 9-hydroxyphenalen-1-one (HPLN) complexesforming adducts with alkali metal ions ([Eu(PLN)3M]+with M = Li, Na, K, Rb, and Cs) confined in a quadrupoleion trap for study. The mass selected alkali metal cation adductsdisplay a split hypersensitive 5D0→ 7F2Eu3+emission band. One of the twoemission components shows a linear dependence on the radius of thealkali metal cation whereas the other component displays a quadraticdependence thereon. In addition, the relative intensities of bothcomponents invert in the same order. The experimental results areinterpreted with the support of density functional calculations andJudd–Ofelt theory, yielding also structural information onthe isolated [Eu(PLN)3M]+chromophores. [ABSTRACT FROM AUTHOR]

Enthalpies of formation at both 0 and 298 K were calculatedaccordingto the HEAT (High-accuracy Extrapolated Ab initio Thermochemistry)protocol for the title molecules, all of which play important rolesin combustion chemistry. At the HEAT345-(Q) level of theory, recommendedenthalpies of formation at 0 K are 301.5 ± 1.3, 180.3 ±1.8, and 23.4 ± 1.5 kJ mol–1for vinyl, allyl,and vinoxy, respectively. At 298 K, the corresponding values are 297.3,168.6, and 16.1 kJ mol–1, with the same uncertainties.The calculated values for the three radicals are in excellent agreementwith the corresponding experimental values, but the uncertaintiesassociated with the HEAT values for vinoxy are considerably smallerthan those based on experimental studies. [ABSTRACT FROM AUTHOR]

Ethyl phosphaethyne, C 2 H 5 CP, has been characterized spectroscopically in the gas phase for the first time, employing millimeter- and submillimeter-wave spectroscopy in the frequency regime from 75 to 760 GHz. Spectroscopic detection and analysis was guided by high-level quantum-chemical calculations of molecular structures and force fields performed at the coupled-cluster singles and doubles level extended by a perturbative correction for the contribution from triple excitations, CCSD(T), in combination with large basis sets. Besides the parent isotopologue, the three singly substituted 13 C species were observed in natural abundance up to frequencies as high as 500 GHz. Despite the comparably low astronomical abundance of phosphorus, phosphaalkynes, R-CP, such as C 2 H 5 CP are promising candidates for future radio astronomical detection.

Huge efforts have recently been taken in the derivation of accurate compilations of rovibrational energies of water, one of the most important reference systems in spectroscopy. Such precision is desirable for all water isotopologues, although their investigation is challenged by hyperfine effects in their spectra. Frequency-comb locked noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy (NICE-OHMS) allows for achieving high sensitivity, resolution, and accuracy. This technique has been employed to resolve the subtle hyperfine splittings of rovibrational transitions of H 2 17 O in the near-infrared region. Simulation and interpretation of the H 2 17 O saturation spectra have been supported by coupled-cluster calculations performed with large basis sets and accounting for high-level corrections. Experimental 17 O hyperfine parameters are found in excellent agreement with the corresponding computed values. The need of including small hyperfine effects in the analysis of H 2 17 O spectra has been demonstrated together with the ability of the computational strategy employed for providing quantitative predictions of the corresponding parameters.

We report on the detection of the (10(0)1) ← (00(0)0) vibrational band of gas-phase C3 and the two of its mono (13)C substituted isotopologs in the infrared region around 3200 cm(-1). Additionally, the associated hot band (11(1)1) ← (01(1)0) has been assigned for the parent isotopolog. Spectra have been recorded using a supersonic jet spectrometer with a laser ablation source in combination with a continuous-wave optical parametric oscillator as radiation source. High-level quantum-chemical ab initio calculations have been performed and used to assist the assignment. A combined fit for the vibrational states of C3 found in this study has been done together with previously reported high-resolution data to increase the accuracy of the molecular parameters, especially for the ground state. The vibrational energies are 3260.126, 3205.593, and 3224.751 cm(-1) for the (10(0)1) state of C3, (12)C(13)C(12)C, and (13)C(12)C(12)C, respectively. The (11(1)1) state of C3 has been found to be at 3330.509 cm(-1).

While the experimental (1)H NMR chemical shiftsof the 1-adamantyl cation can be computed within reasonably small error bounds, the usual Hartree-Fock and density functional quantum-chemical computations, as well as those based on rather elaborate second-order Møller-Plesset perturbation theory, fail to reproduce its experimental (13)C NMR chemical shifts satisfactorily. This also is true even if the NMR shielding calculations treat electron correlation adequately by the coupled-cluster singles and doubles model augmented by a perturbative correction for triple excitations (i.e., at the CCSD(T) level) with quadruple-ζ basis sets. We demonstrate that good agreement can be achieved if highly accurate 1-adamantyl cation equilibrium geometries based on parallel computations of CCSD(T) gradients are employed for the NMR shielding computations.