Vibrational Spectra and Force Constants for Nitrosyl Fluoride and 15N and 18O Species

From infrared absorption studies in the gaseous phase, the fundamental harmonic vibrational frequencies have been determined for 16O14NF, 16O15NF, 18O14NF, and 18O15NF. Two quite different force constant solutions were obtained in a general quadratic valence force field. With the aid of centrifugal distortion constants and the inertial defect, it was possible to select the true force constant solution: FNO=15.9 mdyn Å−1; FNF=2.3 mdyn Å−1; Fα=1.8 mdyn·Årad−2; FNO,NF=2.5 mdyn Å−1; FNO,α=0.27 mdyn rad−1; FNF,α=0.20 mdyn rad−1. These force constants were converted to those of a modified Urey—Bradley force field and a general quadratic central force field. It is shown that the latter gives unreasonable force constants. Interaction displacement coordinates were calculated and correlated qualitatively with valence-bond theory.