Mise au point. Theorie des effets de couplage vibronique multimodes. Probleme a 2 etats. Couplage vibronique mettant en jeu des modes et des etats degeneres. Effets du couplage vibronique multimodes en spectroscopie. Comportement statistique des niveaux d'energie vibroniques. Intersections coniques et evolution temporelle de la fluorescence

Multimode molecular dynamics beyond the Born-Oppenheimer approximation

Multimode Molecular Dynamics Beyond the Born‐Oppenheimer Approximation

The heat of formation of NCO has been determined rigorously by state‐of‐the‐art ab initio electronic structure methods, including Mo/ller–Plesset perturbation theory from second through fifth order (MP2–MP5) and coupled‐cluster and Brueckner methods incorporating various degrees of excitation [CCSD, CCSD(T), BD, BD(T), and BD(TQ)]. Five independent reactions were investigated to establish a consistent value for ΔHf,0○(NCO): (a) HNCO(X 1A’)→H(2S)+NCO(2Π), (b) HNCO(X 1A’)→H++NCO−, (c) N(4S)+CO→NCO(2Π), (d) HCN+O(3P)→H(2S)+NCO(2Π), and (e) NH(3Σ−)+CO→H(2S)+NCO(2Π). The one‐particle basis sets employed in the study were comprised of as many as 377 contracted Gaussian functions and ranged in quality from [4s2p1d] to [14s9p6d4f] on the (C,N,O) atoms and from [2s1p] to [8s6p4d] on hydrogen. After the addition of bond additivity corrections evaluated from related reactions of precisely known thermochemistry, all five approaches were found to converge on the value ΔHf,0○(NCO)=31.4(5) kcal mol−1. Appurtenant refi...

The heat of formation of NCO

In continuing pursuit of thermochemical accuracy to the level of 0.1 kcal mol−1, the heats of formation of NCO, HNCO, HOCN, HCNO, and HONC have been rigorously determined using state-of-the-art ab initio electronic structure theory, including conventional coupled cluster methods [coupled cluster singles and doubles (CCSD), CCSD with perturbative triples (CCSD(T)), and full coupled cluster through triple excitations (CCSDT)] with large basis sets, conjoined in cases with explicitly correlated MP2-R12/A computations. Limits of valence and all-electron correlation energies were extrapolated via focal point analysis using correlation consistent basis sets of the form cc-pVXZ (X=2–6) and cc-pCVXZ (X=2–5), respectively. In order to reach subchemical accuracy targets, core correlation, spin-orbit coupling, special relativity, the diagonal Born–Oppenheimer correction, and anharmonicity in zero-point vibrational energies were accounted for. Various coupled cluster schemes for partially including connected quadrupl...

Toward subchemical accuracy in computational thermochemistry: focal point analysis of the heat of formation of NCO and [H,N,C,O] isomers.

The 266 nm photoelectron spectra of CN−, NCO−, and NCS− have been recorded with a pulsed time‐of‐flight photoelectron spectrometer The photoelectron spectrum of CN− has also been recorded at 213 nm revealing transitions to the A 2Π state as well as the ground X 2Σ+ state of the CN radical The following adiabatic electron affinities (EAs) are determined: EA(CN)=3862±0004 eV, EA(NCO)=3609±0005 eV, and EA(NCS)=3537±0005 eV The adiabatic electron affinity of cyanide is in disagreement with the currently accepted literature value Our measurement of the electron affinity of NCS confirms recent theoretical estimates that dispute the literature experimental value By Franck–Condon analysis of the vibrational progressions observed in each spectrum, the change in bond lengths between anion and neutral are also determined For NCO− this yields R0(C–N)=117±001 A and R0(C–O)=126±001 A, and for CN− the equilibrium bond length is found to be Re(C–N)=1177±0004 A The gas phase fundamental for CN− is deter

http://bromine.cchem.berkeley.edu/grppub/pes17.pdf

Photoelectron spectroscopy of CN−, NCO−, and NCS−

The $\tilde{A}$ $^{2}\Sigma ^{+}$-$\tilde{X}$ $^{2}\Pi \_{\text{i}}$(a) absorption system of the NCO free radical has been re-investigated with higher resolving power than in the earlier work of Dixon (1960). Particular emphasis has been directed to the rotational analyses of bands involving the three vibronic levels, $\mu ^{2}\Sigma ^{(+)}$, $^{2}\Delta \_{i}$(a) and k$^{2}\Sigma ^{(-)}$,, associated with the first level of the bending vibration in the ground state. A misassignment in the earlier work has been corrected and a new value for the Renner parameter determined, namely $\epsilon $ = -0.144 $\pm $ 0.001. This revised value removes the discrepancy noted in the earlier electron resonance results.

P. S. H. Bolman

Papers

A Re-Investigation of the $\tilde{A}$ $^{2}\Sigma ^{+}$-$\tilde{X}$ $^{2}\Pi _{\text{i}}$ Band System of NCO

The Renner—Teller effect and vibronically induced bands in the electronic spectrum of NCO