Collisional reorientation of symmetric-top molecules in stark fields

✍ Scribed by Wan-Ping Hu; Sean A. Harris; Peter W. Harland; Leon F. Phillips

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 221 KB
• Volume: 71
• Category: Article
• ISSN: 0020-7608
• DOI: 10.1002/(sici)1097-461x(1999)71:1<75::aid-qua8>3.0.co;2-g

✦ Synopsis

Calculated cross sections for collisional defocusing of a beam of symmetric-top molecules in a hexapole field are compared with new and recent experimental values. The calculations show that collision processes involving changes in K have much smaller cross sections than those for changing M, and cross sections for changing J are smaller still. The beam defocusing produced by collisions with a background gas that is not the same species as the molecules in the beam occurs mainly as a consequence of ⌬ M transitions induced by a time-varying field which comprises the dipole-induced dipole potential and the anisotropic part of the London potential between the symmetric top and its collision partner. Because the dipole᎐dipole potential depends on 1rr 3 , its time variation is much slower, and so it is much less effective than the potentials which vary as 1rr 6 at inducing transitions by this mechanism during long-Ž . Ž . range ;1 nm collisions at moderate relative velocity ;500 mrs .