The Infrared Spectrum and Internal Rotation Barrier in HF--BF3

Published

May 1, 2000

Author(s)

K Nauta, R E. Miller, Gerald T. Fraser, Walter J. Lafferty

Abstract

The rotationally resolved infrared spectrum of the HF stretch fundamental in combination with one quantum of internal rotationexcitation has been observed for the HF--BF₃ complex using a color-center-laser optothermal molecular-beam spectrometer.This study builds on a previous microwave investigation of the rotational spectrum of the ground vibration-internal rotor state (m= 0) by Phillips et al. [J. Am. Chem. Soc. 117, 12549 (1995)] which revealed a nearly symmetric top, with the HF fluorine lyingalong the BF₃ three-fold symmetry axis (C₃). The microwave study also indicated that the HF axis is nearly orthogonalwith the BF₃ C₃ axis, with the proton undergoing nearly free rotation about this axis. In the present investigation, theinfrared band origin is observed at 3957.54397(21) cm^-1 and is red-shifted by only 3.9 cm^-1 from the HF monomer origin.A consequence of the nearly free rotation is that the band resembles the perpendicular band of a symmetric top, with both the m = 1 first excited and m = 0 ground internal-rotor states well characterized by symmetric-top Hamiltonians. The magnitude of theCoriolis interaction in the doubly degenerate m = 1 internal rotor state observed in combination with the HF stretch is |2Az| =0.61258(6) cm^-1 and corresponds to a barrier to internal rotation of 54 cm^-1 in the HF stretch excited state.

Citation

Chemical Physics Letters

Volume

322

Issue

No. 5

Pub Type

Journals

Keywords

barrier to internal rotation, HF--BF₃ complex, infrared spectrum, molecular beam spectrometer, nearly free internal rotation, vibration rotation constants

Citation

Nauta, K. , Miller, R. , Fraser, G. and Lafferty, W. (2000), The Infrared Spectrum and Internal Rotation Barrier in HF--BF₃, Chemical Physics Letters (Accessed April 30, 2024)