Stark and Zeeman effects in ethylene observed by sub-Doppler infrared spectroscopy

Publisher Website
Google Scholar
Abstract
The recent development of sub-Doppler spectroscopy using microwave modulation sidebands on CO2 laser radiation has enabled us to perform ultrahigh resolution tunable infrared spectroscopy and study the Stark and Zeeman effects in ethylene. Clear Stark splittings were observed in low J vibration–rotation transitions of the ν7 band by applying an electric field of up to 50 kV/cm. The Stark shift is caused by the polarizability of ethylene as well as by the second order Stark effect between the accidentally degenerate ν7 and ν8 vibrational states (ν07−ν08 =8.91 cm−1). Analysis of the observed Stark patterns gives the polarizability anisotropies for the ground state to be αaa− 1/2 (αbb+αcc) =1.91(13) Å3 and αbb−αcc =0.07(19) Å3 and for the ν7 state to be αaa− 1/2 (αbb+αcc) =1.78(11) Å3 and αbb−αcc =0.15(14) Å3. The dipole moment along the a axis of ethylene induced by the ν7 and ν8 vibrations was determined to be ∂2μa/∂q7 ∂q8 =0.0791(4) D. Zeeman splittings of ethylene in a magnetic field of approximately 2.5 kG were also observed. Since the infrared radiation was right-handed circularly polarized and the axial magnetic field was along the direction of the beam, only the Δm=+1 transitions were observed. The tensor components of the rotational g factors were determined to be gaa =−0.424(8), gbb =−0.123(8), and gcc =0.037(6). A qualitative discussion on the relationship of the electronic structure of ethylene and the rotational g factors is given.