Internal Motion in Lithium Tetrahydroborate LiBH4

✍ Scribed by Eizi Hirota; Yoshiyuki Kawashima

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 143 KB
• Volume: 181
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1996.7191

✦ Synopsis

A vibrational satellite of the rotational spectrum of lithium tetrahydroborate LiBH 4 , which was assigned to the first excited torsional state of the BH 4 group, showed two types of anomalies, and they were explained by the interaction of the torsional motion with the overall rotation. The first anomaly, a ''2,01'' interaction constant r t large compared with the ''2,2'', i.e., l-type doubling, constant q t , was ascribed to the cubic anharmonic potential constant k ttt , which is anomalously large because of the unique shape of the potential function for the BH 4 torsion, and to the large dependence of the xz and yz cross products of inertia on the torsional coordinate. The second anomaly, a sizable increase in the D JK centrifugal distortion constant with excitation of the torsional mode, was accounted for in a similar way by anomalously large cubic k ttt and quartic f tttt anharmonic terms in the torsional potential function. The harmonic and anharmonic potential constants chosen so as to explain the anomalies were favorably compared with those estimated from a multipole expansion of the potential function.