Rotational Spectrum of Sarin

✍ Scribed by A.R.Hight Walker; R.D. Suenram; Alan Samuels; James Jensen; Michael W. Ellzy; J.Michael Lochner; Daniel Zeroka

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 192 KB
• Volume: 207
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.2001.8307

✦ Synopsis

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., 1 σ ), 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-foldsymmetry 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.