Structure, ab initio harmonic force field and infrared spectrum of CH3C As

The experimental r(z) and r(e) structures of ethylidynearsine, CH3C=As, wer e calculated using the experimental ground state rotational constants of ei ght isotopic species and an ab initio harmonic force field calculated at th e B3LYP/6-311++G(3df,2pd) level and scaled using the experimental centrifug al distortion constants. For comparison the structure was calculated ab ini tio at the MP2 level. The average geometry is: r(z)(C-H) = 1.097 (2) Angstr om, r(z)(C-C) = 1.467 (2) Angstrom, r(z)(C=As) = 1.659 (2) Angstrom, angle( z)(HCC) = 110.6 (2)degrees and the equilibrium one: r(e)(C-H) = 1.091 (3) A ngstrom, r(e)(C-C) = 1.465 (2) Angstrom, r(e)(C=As) = 1.658 (2) Angstrom, a ngle(e)(HCC) = 110.6 (2)degrees. The infrared spectrum was studied at low r esolution and the analysis of the nu(4) band investigated by high resolutio n Fourier transform spectroscopy is presented. The center of the band was f ound at 627.913 289 (44) cm(-1). (C) 1999 Elsevier Science B.V. All rights reserved.