5314027769

POSTER SESSION. H23

TRIPLE TRANSITIONS IN SOLID HYDROGEN, DEUTERIUM AND HD

M. MENCEL, B. P. W1NNEWISSER AND M. WINNE-WISSER. Physikalisch-Chemisches Institut. Justus-Liebuj-Umversitat, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany.

The infrared absorption spectrum of the solid hydrogens is well understood in terms of a pairwise multipolar induction mcchanism leading to the infrared activity of single and double transitions. Our measurements of such transitions in H > have been extended to D2 and HD in the near infrared region. Furtherinorc. in recent expcriments we havc identified various triple transitions for the first tiine ⁰ 6.

There are two basie concepts for the siniultaneous excitation of three hydrogen molecules upon absorption of radiation:

•    Intensity transfer due to mixing of States,

•    Three-body induced dipole moments.

The infrared activity of triple transitions by intensity transfer due to mixing of States was suggested by Tipping et a i. ^c As an ex ample of this concept we present the transitions Q1 (0) + Qi (0) + S₀(0) and Si(0) + Q1 (0) + So(0) in both solid hydrogen and deuterium. However, with this concept it is not possible to explain the triple transition Sj(0) + Q1 (0) 4- Qi(0) which we have also observed in crystals of H_k>. D2 and HD.

We present a theory of three-body induced dipole moments in order to account for the linestrength of tłiis very remarkable transition.

°M. Mcngcl. B P. Winnewisscr. and M. Winnewisser, .1. Mol. Spoctrosc. 188. 221 241 (1998). 'M. Mengel, B P. Winnewisser. and M. Winnewisser, ,1. Low Temp. Phys. (Proceedings of the Cryocrystal '97 Conferencc), in press, (1998).

^CH.H Tipping. Q. Ma, and J.D. Poll, Phys. Rev. B 22. 12314 12317 (1991).