Abstract
Microwave sidebands of CO2 laser lines were used as an infrared source in infrared microwave double resonance spectroscopy and infrared saturation spectroscopy to study the C-O stretching fundamental band of methanol. In the former application, rotational lines in the vCO = 1 state have been observed with good signal to noise ratios and physical processes involved in this method have been discussed. In the latter method, (vt, A/E, K) = (2, A, 4) sequence transitions in the C-O stretching fundamental band have been identified and term values for the (2, A, 4) levels in the vCO = 1 state have been determined.
Highlights
Microwave sidebands of CO2 laser lines are useful infrared sources for spectroscopy in the 10-μm region due to their tunability, high power and high spectral purity
This band has been studied by infrared Fourier transform (FT) spectroscopy [1] and the data given in Ref. [1] are widely used
To have higher infrared powers in the cell, a desired sideband was separated from the carrier not before but after the beam passed through the cell by the Fabry-Perot filter and was detected by an infrared detector followed by a lock- in-amplifier locked to 100 kHz
Summary
Microwave sidebands of CO2 laser lines are useful infrared sources for spectroscopy in the 10-μm region due to their tunability, high power and high spectral purity. A transition moment for a vibration-rotational transition μ is given by μvΦR [2], where dipole moment μv and direction cosine ΦR are related to the change of the vibrational state and that of rotational state, respectively; as typical values, μv and ΦR are assumed to be 0.1 D and 1/3, respectively This transition is saturated when μE/h ~∆ν, where E is the amplitude of the laser electric field, μE/h is the Rabi- frequency of this transition, and ∆ν is the collisio nal width (HWHM). In case the rotational transition is in the vCO = 1 state of CH3OH, a strong double resonance signal is observed when the infrared transition is saturated.
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