An experimental study of collision broadening of rotational spectral lines of 13CH3 13C15N in the ground and nν8, n=1 and 2 vibrationally excited states at microwave frequencies

Abstract

A double modulation microwave spectrometer was used to determine the linewidth parameter for some rotational components in the nν8 vibrations of methyl cyanide under 13C and 15N substitution. The linewidth parameters for self-broadening of the ΔJ=2←1 rotational components for the ground, ν8, and 2ν8 vibrations were determined over a pressure range of 1–13 mTorr and at a temperature of 300 K. An experimental method is presented to correct for modulation broadening when high derivatives are used to extract the absorption profile information from the signals. The eighth derivative profile was explored to determine if the spectral line shape remains Lorentzian over a range of modulation levels from 10% of Δν to more than 100% of Δν. These tests showed that the ratio of inner to next inner peak separations, designated in this paper as Δ, of the eighth derivative was the same as that for an assumed Lorentzian line shape. Thus, line shapes were assumed to be Lorentzian for theoretical analysis of the derivative profiles and comparisons made between experiment and theory on that basis. Dipole moments for vibrationally excited energy levels for the ν8 and 2ν8 vibrations were calculated from the linewidth parameter data after all corrections had been made for modulation, Doppler, and other nonpressure broadening effects.

K-Dependence and temperature dependence of N2-, H2-, and He-broadening coefficients for the J=12–11 transition of acetonitrile CH3C14N located near 220.7GHz

“…They were all related to rather low Jvalues. In the microwave and millimeter-wave ranges, most previous works concern self-relaxation: the self-broadening parameters were reported for the (J, K) = (2, 0) and (2, 1) rotational components of 13 CH 3 13 C 15 N isotopic species investigated in various vibrational states [13], and for the (J, K) = (1, 0), (2, 0), and (3, 2) rotational components of CH 3 C 15 N variety [14]. Pressure shift and broadenings of the J = 1, 2, 3, 4, and 6 rotational transitions of CH 3 CN were measured and results can be found in Ref.…”