Dept. of Chemistry University of Arizona A. Janczyk L. M. Ziurys The Millimeter/Submillimeter Spectrum of AlSH (X 1 A) : Further Investigation of the Metal Hydrosulfide Structures ~

Outline  Motivation for the Aluminum hydrosulfide project  Experimental procedure  Results  Structural parameters  Conclusion

A Search for AlSH toward IRC ? AlNC, AlF and AlCl have been observed toward the late carbon star IRC Given the presence of these closed shell species AlSH may be present in the IRC as well. IRC Composite B+V image of the highly evolved star by Mauron & Huggins (1999), which shows multiple shell structure within the extended circumstellar envelope. Mauron and Huggins estimate this shell represents the mass loss history over the past 10,000 years, with density enhancements ejected each few hundred years, corresponding to thermal pulse timescales.

MOH Periodic trends

MSH Periodic trends

Low Temperature Spectrometer Block Diagram

Experimental conditions for AlSH

Diagram of the Broida Type Oven

AlSH (X 1 A): J=27  26 (K a,K c ) ~

AlSD (X 1 A): J=29  28 (K a,K c ) ~

AlSH (X 1 A): J = 26  27 : K a Components ~ K a = 5 and 6 are perturbed

Observed Rotational Transitions of AlSH and AlSD AlSH – 9 transitions, 117 lines were measured AlSD – 7 transitions, 81 lines were measured

Rotational constants for AlSH and AlSD H = H rot + H cd

* * value is given in MHz Perturbation via rotation  vibration coupling J = 26  27

Perturbation via rotation  vibration coupling The perturbation is attributed to the rotation-vibration coupling. As the molecule rotates faster about the a-axis it becomes more bent and therefore couples more effectively to the bending mode. This effect can be tested by calculating the K a dependent rotational constant via the following expression. The constant D K was scaled from the value for CaSH and CaSD by the ratio of rotational constants resulting in D K (AlSH) = 16.6 MHz and D K (AlSD)=6.6 MHz. From K a = 0 to K a = 6 the A eff and B eff decrease making the molecule more bent and coupling it to the bending vibrational mode.

The Coriolis term is thought to be small for simple molecules such that the major contribution to the inertial defect is harmonic.   0 = I c -I a -I b  0 (AlSH ) = amu Å 2 and  0 (AlSD ) = amu Å 2 The molecular nonrigidity contributes to the effective moment of inertia. Inertial deffect The experimental inertial defect, which consists of a harmonic and Coriolis term was calculated.

 2 ( AlSH ) = 430 cm -1 and  2 ( AlSD ) = 318 cm -1 The effective frequency agrees very well with theoretical bending frequency  2 ( AlSH ) = cm -1. (Xian-Yang Chen et al.,2000)  The bending frequency is the most influential in contributing to the molecular nonrigidity in case of AlSH. Inertial deffect A simple approximation attributes the major part of the inertial defect to the lowest in-plane vibration. amu Å 2 cm -1

AlSH and other M-SH r 0 structures STRFIT,Kisiel Z J.Mol. Spectrosc. 218, 58

MSH Periodic trends Al

AlOH and AlSH r 0 structures

 Aluminum hydroxide is on average linear in the ground electronic state.  The bonding is thought to be ionic  Aluminum hydrosulfide is bent in its ground electronic state with  Al-S-H = 88.5 . The almost octahedral angle indicates that S bonds to H and Aluminum over the p x and p y orbitals.  Bonding in AlSH has a covalent character  AlSH does not deviate significantly from  H-S-H = 92.1   the bonding mechanism is not affected by substituting H with Al in H 2 S. Conclusions — AlOH/AlSH

Acknowledgments  Dr. Lucy Ziurys  Dr. Ziurys group  This research was supported by NSF Grant CHE