A He(I) Photoelectron Spectroscopic Study of the X2A"2state of NH3+ and ND3+. A Reanalysis and evidence for the Coriolis Coupling between the Bending nu2 and nu4 Modes.
[en] In the He(I) photoelectron spectrum of NH3 and its isotopomer ND3 the complete vibrational structure of the X2A"2 state of NH3+ and ND3+ is examined in detail. Three vibrational progressions are identified. The well-known strongest progression, already unambiguously assigned to the nu2 out-of-plane bending mode, is observed from v=0-17 in NH3+ and v=0-20 in ND3+. For NH3+ this vibration could be characterized not only by its energy hcomega2= 0.109+/-0.001 eV (or omega2= 878+/-7 cm-1) but also by its first anharmonicity constant hcomega22x22=-(16.2+/-1.2)10-4 eV (or omega22x22=-13.0+/-1.0 cm-1). The best fit of the experimental data required the introduction of a second anharmonicity constant, i.e. hcomega22y22= -(30.7+/-4.2)x10-6 eV (or omega22y22=-0.248+/-0.034 cm-1). The earlier reported weak progression assigned to the vibrational combination nu1+nnu2 transitions has been reexamined. Suitable handling of the data leads to two possible energies for the nu1 degenerate NH stretching vibrational normal mode, i.e. hcomega1 =0.306+/-0.006 eV or 0.422+/-0.005 eV. Several arguments are brought to favour the value of hcomega1=0.422 eV (or omega1=3404 cm-1). Finally a third weak progression, reported for the first time, is assigned to nu4+nnu2 transitions where the nu4 in-plane bending mode is optically forbidden. This vibrational normal mode is characterized by an energy hcomega4=0.186+/-0.010 eV (omega4=1500+/-80 cm-1). In agreement with the theoretical predictions, this transition becomes allowed through a strong Coriolis vibro-rotational coupling between the nu4 and the nu2 vibrational normal modes. The same measurements and the isotope effect on the molecular constants are investigated in ND3+ too.
Research center :
Laboratoire de Dynamique Moléculaire
Disciplines :
Chemistry
Author, co-author :
Locht, Robert ; Université de Liège - ULiège > Département de Chimie (Faculté des sciences) > Laboratoire de Dynamique Moléculaire (Sciences)
Leyh, Bernard ; Université de Liège - ULiège > Département de chimie (sciences) > Laboratoire de dynamique moléculaire
Hottmann, K.
Baumgärtel, H.; Freie Universität Berlin > Institut für Physikalische Chemie
Language :
English
Title :
A He(I) Photoelectron Spectroscopic Study of the X2A"2state of NH3+ and ND3+. A Reanalysis and evidence for the Coriolis Coupling between the Bending nu2 and nu4 Modes.
Alternative titles :
[fr] Une étude de l'état X2A"2 de NH3+ et ND3+ par la spectroscopie photoélectronique à He(I). Une révision et une évidence en faveur d'un couplage de Coriolis entre les modes de bending nu2 et nu4.