No abstract

group in this state of PhN. This delocalization is favorable energetically because in 2 the non bonding and electrons have opposite spins, so that the motions of these two electrons are not correlated by the Pauli exclusion principle. Hence, in the ' state of HN these two nonbonding electrons have a large Coulombic repulsion energy.14 However, in PhN, delocalization of the electron into the phenyl group allows these two electrons to occupy different regions of space, thus minimizing their Coulombic repulsion energy.14•15 In carbenes, too, an adjacent ir bond provides selective stabilization for the open-shell singlet state (1A").16,17Despite the selective stabilization of !A2 in PhN, we still compute it to lie about 18 kcal/mol above the 3A2 ground state. As shown in Table I, neither this calculated energy difference nor that between the ' and 32" states of NH shows much sensitivity to the amount of electron correlation provided.As is the case in calculations on methylene,18 the results of our calculations and previous12 calculations on HN suggest that very large basis sets appear to be necessary to correlate the two electrons lations were performed. We also thank the San Diego Supercomputer Center for a generous allocation of computer time, Professor Matthew S. Platz for conversations that stimulated this computational study, Professor G. Barney Ellison for agreeing to simultaneous publication, and Professor Richard N. McDonald for communicating his results to us in advance of publication.

We have observed the negative ion photoelectron spectrum of the methylnitrene ion, CH3N−, and measured the electron affinity of methylnitrene, EA(CH3N)=0.022±0.009 eV. In addition to detaching the methylnitrene anion to the ground state of CH3N(X̃ 3A2), we also detect the first electronically excited state of methylnitrene, ã 1E. We measure the singlet/triplet splitting to be ΔE(ã 1E−X̃ 3A2)=1.352±0.011 eV. The photoelectron spectrum of CH3N ã 1E contains relatively sharp vibronic structure. Unlike the spectra from H2CC−, the photoelectron spectra for CH3N− show no evidence for a barrier separating the rearrangement of singlet methylnitrene to methyleneimine, [CH31N] → CH2=NH.

Erratum: Application of a coupled-surface time-dependent Hartree grid method to excited state optical spectroscopy [J.

We have measured the negative ion photoelectron spectra of CH2N− and CD2N− and find the electron affinities: EA(CH2N)=0.511±0.008 eV and EA(CD2N)=0.498±0.011 eV. Franck–Condon simulations of these spectra are carried out and we estimate the CH2N− and CH2N geometry differences; we fit our spectra with the following [constrained] molecular structures. We combine our EA(CH2N) with the results of previous gas phase ion studies to extract a number of thermochemical parameters (kcal/mol): Do0(CH2N–H)=85±5, Do0(H–HCN)=23±6, Do0(H2C–N)=144±6, and the isomerization enthalpy of H2CN+→HCNH+ is ΔHisom(C2v→C∞v)=−51±7. Attempts to calculate the geometry and vibrational frequencies of the H2CN radical are disappointing. Unrestricted Hartree–Fock and second-order Mo/ller–Plesset ab initio calculations in a 6-31++G** basis produce badly spin-contaminated wave functions which do not reproduce the experimental findings.