title: Rotational Spectrum of Sarin.
abstract: As part of an effort to examine the possibility of using molecular-beam Fourier-transform microwave spectroscopy to unambiguously detect and monitor chemical warfare agents, we report the first observation and assignment of the rotational spectrum of the nerve agent Sarin (GB) (Methylphosphonofluoridic acid 1-methyl-ethyl ester, CAS #107-44-8) at frequencies between 10 and 22 GHz. Only one of the two low-energy conformers of this organophosphorus compound (C(4)H(10)FO(2)P) was observed in the rotationally cold (T(rot)<2 K) molecular beam. The experimental asymmetric-rotor ground-state rotational constants of this conformer are A=2874.0710(9) MHz, B=1168.5776(4) MHz, C=1056.3363(4) MHz (Type A standard uncertainties are given, i.e., 1sigma), as obtained from a least-squares analysis of 74 a-, b-, and c-type rotational transitions. Several of the transitions are split into doublets due to the internal rotation of the methyl group attached to the phosphorus. The three-fold-symmetry barrier to internal rotation estimated from these splittings is 677.0(4) cm(-1). Ab initio electronic structure calculations using Hartree-Fock, density functional, and Moller-Plesset perturbation theories have also been made. The structure of the lowest-energy conformer determined from a structural optimization at the MP2/6-311G(**) level of theory is consistent with our experimental findings. Copyright 2001 Academic Press.
authors.affiliation: Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899
authors.forename: A. R. Hight
authors.initials: AR
authors.lastname: Walker
authors.forename: R. D.
authors.initials: RD
authors.lastname: Suenram
authors.forename: Alan
authors.initials: A
authors.lastname: Samuels
authors.forename: James
authors.initials: J
authors.lastname: Jensen
authors.forename: Michael W.
authors.initials: MW
authors.lastname: Ellzy
authors.forename: J. Michael
authors.initials: JM
authors.lastname: Lochner
authors.forename: Daniel
authors.initials: D
authors.lastname: Zeroka