FTIR Spectroscopy of Small Titanium-Carbides A Survey and Preliminary Results Robin Kinzer TCU Molecular Physics Laboratory 31 October 2005

Background & Previous Research

Background - Titanium Titanium exists in five stable isotopes, Ti. 48 Ti is most common (73.7%); radioactive 44 Ti is produced almost exclusively in supernova. Titanium exists in five stable isotopes, Ti. 48 Ti is most common (73.7%); radioactive 44 Ti is produced almost exclusively in supernova. Ti composes 80 ppb/atom in the universe and 100 ppb/atom of the sun. Carbonaceous meteorites contain 230,000 ppb/atom. Ti composes 80 ppb/atom in the universe and 100 ppb/atom of the sun. Carbonaceous meteorites contain 230,000 ppb/atom. By comparison, gold is and 0.01 ppb/atom for universe and sun, respectively; iron is 20,000 and 30,000 ppb/atom, respectively. Iron is 7.7 x 10 6 ppb/atom in meteorites. By comparison, gold is and 0.01 ppb/atom for universe and sun, respectively; iron is 20,000 and 30,000 ppb/atom, respectively. Iron is 7.7 x 10 6 ppb/atom in meteorites. Data from:

Background - Titanium M stars, the coolest stars, are notable for having very strong molecular absorption bands, particularly TiO (Carrol & Ostlie, p. 226). M stars, the coolest stars, are notable for having very strong molecular absorption bands, particularly TiO (Carrol & Ostlie, p. 226).

Background - Ti 8 C 12 + Observation of C 60 sparked extensive study of other fullerenes. Observation of C 60 sparked extensive study of other fullerenes. The first report of metallocarbohedrenes – cage- like molecules incorporating metals and carbon atoms – was made by Castleman, et al. in Science (1992, v.255, 1411). They reported the discovery of Ti 8 C 12 + via mass spectrometry. The first report of metallocarbohedrenes – cage- like molecules incorporating metals and carbon atoms – was made by Castleman, et al. in Science (1992, v.255, 1411). They reported the discovery of Ti 8 C 12 + via mass spectrometry.

Background - Ti 8 C 12 + Ti 8 C 12 + has dodecahedral (T h ) symmetry and is very stable due to strong Ti-C & C-C  - bonding and its shape. Ti 8 C 12 + has dodecahedral (T h ) symmetry and is very stable due to strong Ti-C & C-C  - bonding and its shape. This ‘metcar’ was formed by reacting Titanium with CH 4, C 2 H 2, C 2 H 4, C 3 H 6, C 6 H 6 vapors. This ‘metcar’ was formed by reacting Titanium with CH 4, C 2 H 2, C 2 H 4, C 3 H 6, C 6 H 6 vapors. Ti 7 C 13 +, Ti 6 C 14 + et al. with similar dodecahedral symmetry are less stable. Ti 7 C 13 +, Ti 6 C 14 + et al. with similar dodecahedral symmetry are less stable.

Background - Research Experimental and theoretical studies of smaller ‘metcar’ structures are needed to better understand how more complex ‘metcars’ form. Experimental and theoretical studies of smaller ‘metcar’ structures are needed to better understand how more complex ‘metcars’ form. Studies include PES observation of TiC x - where x=2-5 and DFT study of the structure of TiC 2, TiC 3 and TiC 4. Studies include PES observation of TiC x - where x=2-5 and DFT study of the structure of TiC 2, TiC 3 and TiC 4. Though these studies concentrate on infrared, experimental studies have yet to observe the fundamental vibrational levels of neutral titanium- carbides. Though these studies concentrate on infrared, experimental studies have yet to observe the fundamental vibrational levels of neutral titanium- carbides.

Background – PES Studies Wang, Ding & Wang researched vibrational PES of TiC x -, x=2-5, using Nd:YAG lasers. Wang, Ding & Wang researched vibrational PES of TiC x -, x=2-5, using Nd:YAG lasers. Ground state for the TiC x - (X) and excited vibrational states of the neutral TiC x (A-D) were observed. Ground state for the TiC x - (X) and excited vibrational states of the neutral TiC x (A-D) were observed. Fundamental vibrations of neutral molecules extrapolated from excited vibrational levels. Fundamental vibrations of neutral molecules extrapolated from excited vibrational levels. Wang, X.B; Ding, C.F; Wang, L.S; J. Phys. Chem. A 1997, 101, nm 532 nm

Background – PES Studies No previous calculations had been made for TiC 3-5 ; prediction for their structures were made by comparing this data to previous YC x and LaC x research. No previous calculations had been made for TiC 3-5 ; prediction for their structures were made by comparing this data to previous YC x and LaC x research. Since the C-C bond is strong and less likely to break than a TiC bond, they predicted ring- like structures for TiC 3-5, similar to YC x and LaC x. Since the C-C bond is strong and less likely to break than a TiC bond, they predicted ring- like structures for TiC 3-5, similar to YC x and LaC x. TiC ± 50 cm -1 TiC ± 30 cm -1 TiC ± 40 cm -1 TiC ± 60 cm -1 Wang, X.B; Ding, C.F; Wang, L.S; J. Phys. Chem. A 1997, 101, Totally symmetric modes.

Background – PES Study Problem: The vibrational fundamental of the neutral molecule is extrapolated from the higher vibrational energy levels. Problem: The vibrational fundamental of the neutral molecule is extrapolated from the higher vibrational energy levels. The reported observations have large margins of error, in the range of cm -1. The reported observations have large margins of error, in the range of cm -1. Note: These are the only results available for TiC 2-5 in the NIST Chemistry WebBook. Note: These are the only results available for TiC 2-5 in the NIST Chemistry WebBook.

Background – DFT Study R. Sumathi and M. Hendrickx published a DFT survey of TiC x, x=2-4, solving ab initio the energy levels of several isomers. R. Sumathi and M. Hendrickx published a DFT survey of TiC x, x=2-4, solving ab initio the energy levels of several isomers. Vibrational frequencies for each isomer and electronic state were solved. Vibrational frequencies for each isomer and electronic state were solved. Calculated frequencies for the optimum isomer were in good agreement with those observed by Wang, et al. Calculated frequencies for the optimum isomer were in good agreement with those observed by Wang, et al. Confirm TiC 2 has C 2v symmetry with a stretching mode at 587 cm -1. Note that Wang, et al. observed 560 ± 50 cm -1. Confirm TiC 2 has C 2v symmetry with a stretching mode at 587 cm -1. Note that Wang, et al. observed 560 ± 50 cm -1.

Background – DFT Study Below: Optimized geometries for singlet, triplet ( ) and quintet [ ] isomers of TiC 3 at the B3LYP level of theory. Bond length in Å. TiC 3 Above: Plot of relative energies (kcal/mol) of the various isomers of TiC 3 in different electronic states.

Background – DFT Study TiC 3 Singlet TiC 4 Triplet Calculated Frequencies: ; ; 833.6; 686.5; 591.2; cm -1 Calculated Frequencies: ; ; ; 601.1; 473.6; 472.2; 399.6; 391.1; cm -1 Observed Frequencies (Wang): ± 650 ± 30 cm -1 Observed Frequencies (Wang): ± 440 ± 40 cm -1

Background – DFT Study This study is exhaustive in considering several possible isomers and electronic states for the chosen molecules. This study is exhaustive in considering several possible isomers and electronic states for the chosen molecules. Unfortunately, this study does not provide estimated intensities for these different modes of TiC 3 and TiC 4. Unfortunately, this study does not provide estimated intensities for these different modes of TiC 3 and TiC 4.

Current Research & Experiment

Experimental Apparatus Nd-YAG 1064 nm pulsed laser Quartz window laser focusing lens Ar To pump Torr or better CsI window To pump Torr Carbon rod Titanium rod gold mirror ~ 10K Bomem DA3.16 Fourier Transform Spectrometer KBr beam splitter liquid N 2 cooled MCT detector ( cm -1 )

Survey Spectrum of Ti + 12 C The following (best) spectra of titanium and graphite ablation were obtained in June The following (best) spectra of titanium and graphite ablation were obtained in June Three bands of interest appear: cm -1, cm -1, cm -1. Three bands of interest appear: cm -1, cm -1, cm -1. These three bands are from one experiment where the laser window nearly broke (hitting the C-rod). Thus, less intense light was hitting the rod, and less Carbon deposited. These three bands are from one experiment where the laser window nearly broke (hitting the C-rod). Thus, less intense light was hitting the rod, and less Carbon deposited. These are the strongest these bands appeared in Ti + 12 C experiments. These are the strongest these bands appeared in Ti + 12 C experiments.

TiC Candidates Experiment: 90 min. deposition 12 C < 2.0 W; Ti~ 2.7 W Anneal 14 – 26 K Spectra at 26 K.

Experimental Technique Metal carbide experiments are best performed using a dual ablation technique. This allows more control over multiple evaporation rates than single-rod ablation. Metal carbide experiments are best performed using a dual ablation technique. This allows more control over multiple evaporation rates than single-rod ablation. Baked 13 C low-enrichment (l.e.) rods, though stronger due to baking, take one month to prepare. Soft rods, which are non-baked, are weaker. Baked 13 C low-enrichment (l.e.) rods, though stronger due to baking, take one month to prepare. Soft rods, which are non-baked, are weaker. Experimental technique needs to be adjusted for limitations of the samples. Soft rods cannot be used at the same laser power or as long as baked rods. Experimental technique needs to be adjusted for limitations of the samples. Soft rods cannot be used at the same laser power or as long as baked rods.

Experimental Technique Problem: Aforementioned TiC candidates appeared weakly using l.e. 13 C rods (if at all!). Problem: Aforementioned TiC candidates appeared weakly using l.e. 13 C rods (if at all!). Baked l.e. 13 C rods were previously used (power ~1.5 W). Signal diminishes quickly. Too little deposition of Ti. Baked l.e. 13 C rods were previously used (power ~1.5 W). Signal diminishes quickly. Too little deposition of Ti. New baked rods not readily available. Soft rods must be utilized. New baked rods not readily available. Soft rods must be utilized. Consider reducing laser power on Carbon rod, in spirit of the Ti- 12 C results. Consider reducing laser power on Carbon rod, in spirit of the Ti- 12 C results.

Experimental Technique Overall effect of reducing laser power on Carbon rod. No annealing – 2200 cm -1. At low power. C 3, C 6, C 9 significantly stronger. Other chains also stronger. Not correct! Weaker! (Used) Baked. 10 min dep. ~1.3 Watts. (New) Soft. 25 min dep. ~0.8 Watts. C3C3 C3C3 C3C3 C9C9 C6C6 C7C7 C7C7 C5C5

Theoretical Results for TiC 3 ~1541 cm -1 ~1506 ~1530 Scaled Values for 1484 cm -1

Experimental Technique C4C4 C 4 (~8%) C4C4 C4C C5C5 C5C5 C5C (~9% 1484) * (~57% 1484) ?? ? Baseline corrected. 40 min dep. 18K.

High Enrichment 13 C Experiment Baseline corrected. 20 min dep. 22K.

Results TiC 3 with C 2v symmetry may have a vibrational mode at cm -1. Better resolution of the shift at 1473 and high enrichment 13 C experiments are needed to confirm this. TiC 3 with C 2v symmetry may have a vibrational mode at cm -1. Better resolution of the shift at 1473 and high enrichment 13 C experiments are needed to confirm this. As of yet, no shifts of the cm -1 or cm -1 band have been observed. As of yet, no shifts of the cm -1 or cm -1 band have been observed. Laser powers of ~0.8 W on the l.e. carbon rod produces small carbon chains abundantly. Longer carbon chains may be constructed by annealing these. Laser powers of ~0.8 W on the l.e. carbon rod produces small carbon chains abundantly. Longer carbon chains may be constructed by annealing these. Low laser power has proven to help in sharpening and obtaining shifts of small metal-carbides, as seen in CrC 3 (Bates). Low laser power has proven to help in sharpening and obtaining shifts of small metal-carbides, as seen in CrC 3 (Bates).

Further Work Resolve the ‘feature’ at 1473 cm -1 as best as possible. Resolve the ‘feature’ at 1473 cm -1 as best as possible. Additional high enrichment 13 C experiments need to be run for the TiC 3 candidate. Some of these will be soft rods. Additional high enrichment 13 C experiments need to be run for the TiC 3 candidate. Some of these will be soft rods. Experiments to study and obtain shifts 624 cm -1 and 915 cm -1 bands are needed. Experiments to study and obtain shifts 624 cm -1 and 915 cm -1 bands are needed.