title: Infrared and microwave spectra of the acetylene-ammonia and carbonyl sulfide-ammonia complexes: a comparative study of a weak C-H···N hydrogen bond and an S···N bond.
abstract: We report a combined high resolution infrared and microwave spectroscopic investigation of the acetylene-ammonia and carbonyl sulfide-ammonia complexes using a pulsed slit-nozzle multipass absorption spectrometer based on a quantum cascade laser and a pulsed nozzle beam Fourier transform microwave spectrometer, respectively. The ro-vibrational transitions of the acetylene-ammonia complex have been measured at 6 μm in the vicinity of the ν(4) band of ammonia for the first time. The previously reported pure rotational transitions have been extended to higher J and K values with (14)N nuclear quadrupole hyperfine components detected and analyzed. The spectral analysis reveals that acetylene binds to ammonia through a C-H···N weak hydrogen bond to form a C(3v) symmetric top, consistent with the previous microwave [Fraser et al., J. Chem. Phys., 1984, 80, 1423] and infrared spectroscopic study at 3 μm [Hilpert et al., J. Chem. Phys., 1996, 105, 6183]. A parallel study has also been carried out for the carbonyl sulfide-ammonia complex whose pure rotational and ro-vibrational spectra at 6 μm have been detected and analyzed for the first time. The spectral and the subsequent structural analyses, in conjunction with the corresponding ab initio calculation, indicate that the OCS-NH(3) complex assumes C(3v) symmetry with S pointing to N of NH(3), in contrast to the T-shaped geometries obtained for the isoelectronic N(2)O-NH(3) and CO(2)-NH(3) complexes.
authors.affiliation: Department of Chemistry, University of Alberta, Edmonton, Canada T6G 2G2.
authors.forename: Xunchen
authors.initials: X
authors.lastname: Liu
authors.forename: Yunjie
authors.initials: Y
authors.lastname: Xu
mesh_terms: D000114:Acetylene / Q000737:chemistry*; D000641:Ammonia / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D006860:Hydrogen Bonding; D008872:Microwaves; D009584:Nitrogen / Q000737:chemistry; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared; D013455:Sulfur / Q000737:chemistry; D013461:Sulfur Oxides / Q000737:chemistry*
chemical_list: D013461:Sulfur Oxides; D013455:Sulfur; D002244:Carbon; D000641:Ammonia; D006859:Hydrogen; C010063:carbonyl sulfide; D009584:Nitrogen; D000114:Acetylene