Analyses of the Vibration–Rotation Bands of HCF3, PF5, and Cyclo-C3H6 by Computer Techniques

Abstract

We have studied the ${\nu }_3$ fundamental of fluoroform at 700 cm⁻¹ with a resolution of 0.3 cm⁻¹, obtaining a contour showing a series of well‐resolved $P$ and $R$ branch “lines.” A rotational analysis is performed which determines the ground‐ and first excited vibrational state rotational and distortion constants. A computer program for the calculation of symmetric‐top parallel band contours is critically tested by comparison of the experimental and calculated envelopes of the ${\nu }_3$ HCF₃ band. The ${\nu }_4$ band of phosphorous pentafluoride at 575 cm⁻¹ is studied with a resolution of 0.5 cm⁻¹ giving an unresolved but well‐defined contour which is analyzed by comparison with calculated contours. The results give P–F axial bond length = 1.581 Å, P–F equatorial bond length = 1.534 Å in the ground vibrational state. The ${\nu }_6$ fundamental of cyclopropane is examined under a resolution of 0.3 cm⁻¹, giving a well‐resolved series of $P$ and $R$ branch “lines.” The $B_0$ value for cyclo‐C₃H₆ found from this band is 0.6688 cm⁻¹, while $C_0\text{\hspace{0.17em}=\hspace{0.17em}0.420}{\mathrm{cm}}^{\text{−1}}$ .