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

We have studied the ν3 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 ν3 HCF3 band. The ν4 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 ν6 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 B0 value for cyclo-C3H6 found from this band is 0.6688 cm−1, while C0 = 0.420 cm−1.