title: Precision Lamb-dip infrared spectra of the C-N stretching band of CH(3)NH(2) with a CO(2)-laser/microwave-sideband spectrometer.
abstract: We report saturation dip spectroscopy in the C-N stretching band of CH(3)NH(2) with a resolution of 0.4 MHz and an accuracy of 0.1 MHz by use of a CO(2)-laser/microwave-sideband spectrometer. The wide tunability, Lamb-dip resolution, absolute frequency accuracy, and high sensitivity of our dual-mode instrument were all key features in making precise measurements for a range of lines in the densely crowded spectrum with its complex pattern of splittings arising from the large-amplitude CH(3) torsion and NH(2) inversion. We focused on achieving resolution and assignment of transitions within the highly blended Q branch of the C-N stretch and on observations of the important K=0 sequences of Aa and Ea torsion-inversion symmetry. Term values of the latter were fitted to J(J+1) power-series expansions to obtain the K=0 C-N stretching effective B values and substate origins, from which calculated ground-state substate energies were subtracted to yield values of 1044.7061 and 1044.8011 cm(-1) for the Aa and Ea subband origins, respectively. We thereby estimate a mean value of 1044.75(5) cm(-1) for the vibrational band origin and 0.7323(5) cm(-1) for the effective upper-state B value for the C-N stretching fundamental of CH(3)NH(2).
authors.affiliation: School of Physics, Shandong University, 250100 Jinan, People's Republic of China. zdsun@sdu.edu.cn
authors.forename: Zhen-Dong
authors.initials: ZD
authors.lastname: Sun
authors.forename: Ronald M
authors.initials: RM
authors.lastname: Lees
authors.forename: Li-Hong
authors.initials: LH
authors.lastname: Xu
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D007834:Lasers; D008744:Methylamines / Q000737:chemistry*; D008872:Microwaves; D013055:Spectrophotometry, Infrared
chemical_list: D008744:Methylamines; D002245:Carbon Dioxide