High-resolution spectroscopy of (CH3OH)-O-18: Stark behavior of FIR laser lines

We report the Stark behavior of 31 FIR laser lines of (CH3OH)-O-18 optically pumped by a CO2 waveguide laser. We observe various behaviors for different laser lines: power decrease, power enhancement, shifting and splitting of the laser lines, or no effect at all. Since the observed Stark line shapes depend critically on the quantum numbers of the molecular levels involved in the laser cycle, we used the Stark effect to test many of the known assignments of FIR laser lines of (CH3OH)-O-18. Nineteen previous assignments were confirmed and a new one is proposed. Two new laser lines are also reported and characterized in wavelength, offset and polarization. The linear Stark shifts were calculated including both the usual first-order mu(a)-type terms and the mu(b)-type contributions arising from the mixing of Stark and molecular asymmetry terms. This second term is incorporated in the calculations by writing mu(n, tau, K, J) = mu(a)S(b)(n, tau, K J), where S-b(n, tau, K, J) is a state-dependent scaling factor close to unity. (C) 1996 Academic Press, Inc