FTIR Spectroscopy of FTIR Spectroscopy of Small Titanium-Small Titanium-

CarbidesCarbidesA Survey and Preliminary ResultsA Survey and Preliminary Results

Robin KinzerRobin KinzerTCU Molecular Physics LaboratoryTCU Molecular Physics Laboratory

31 October 200531 October 2005

Background & Previous Background & Previous ResearchResearch

Background - TitaniumBackground - Titanium Titanium exists in five stable isotopes, Titanium exists in five stable isotopes, 46-46-

5050Ti. Ti. 4848Ti is most common (73.7%); Ti is most common (73.7%); radioactive radioactive 4444Ti is produced almost Ti is produced almost exclusively in supernova.exclusively in supernova.

Ti composes 80 ppb/atom in the universe Ti composes 80 ppb/atom in the universe and 100 ppb/atom of the sun. Carbonaceous and 100 ppb/atom of the sun. Carbonaceous meteorites contain 230,000 ppb/atom.meteorites contain 230,000 ppb/atom.

By comparison, gold is 0.004 and 0.01 By comparison, gold is 0.004 and 0.01 ppb/atom for universe and sun, ppb/atom for universe and sun, respectively; iron is 20,000 and 30,000 respectively; iron is 20,000 and 30,000 ppb/atom, respectively. Iron is 7.7 x 10ppb/atom, respectively. Iron is 7.7 x 1066 ppb/atom in meteorites.ppb/atom in meteorites.

Data from: www.webelements.com

Background - TitaniumBackground - Titanium

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

Background - TiBackground - Ti88CC1212++

Observation of CObservation of C6060 sparked extensive sparked extensive study of other fullerenes. study of other fullerenes.

The first report of The first report of metallocarbohedrenes – cage-like metallocarbohedrenes – cage-like molecules incorporating metals and molecules incorporating metals and carbon atoms – was made by Castleman, carbon atoms – was made by Castleman, et al.et al. in in ScienceScience (1992, v.255, 1411). (1992, v.255, 1411). They reported the discovery of TiThey reported the discovery of Ti88CC1212

++ via mass spectrometry.via mass spectrometry.

Background - TiBackground - Ti88CC1212++

TiTi88CC1212+ + has dodecahedral has dodecahedral

((TThh) symmetry and is very ) symmetry and is very stable due to strong Ti-C stable due to strong Ti-C & C-C & C-C -bonding and its -bonding and its shape.shape.

This ‘metcar’ was formed This ‘metcar’ was formed by reacting Titanium with by reacting Titanium with CHCH44, C, C22HH22, C, C22HH44, C, C33HH66, , CC66HH66 vapors. vapors.

TiTi77CC13 13 ++, Ti, Ti66CC14 14

++ et alet al. with . with similar dodecahedral similar dodecahedral symmetry are less stable.symmetry are less stable.

Background - ResearchBackground - Research

Experimental and theoretical studies of Experimental and theoretical studies of smaller ‘metcar’ structures are needed to smaller ‘metcar’ structures are needed to better understand how more complex better understand how more complex ‘metcars’ form.‘metcars’ form.

Studies include PES observation of TiCStudies include PES observation of TiCxx--

where x=2-5 and DFT study of the structure where x=2-5 and DFT study of the structure of TiCof TiC22, TiC, TiC33 and TiC and TiC44..

Though these studies concentrate on infrared, Though these studies concentrate on infrared, experimental studies have yet to observe the experimental studies have yet to observe the fundamental vibrational levels of neutral fundamental vibrational levels of neutral titanium-carbides.titanium-carbides.

Background – PES Background – PES StudiesStudies

Wang, Ding & Wang Wang, Ding & Wang researched vibrational researched vibrational PES of TiCPES of TiCxx

--, x=2-5, using , x=2-5, using Nd:YAG lasers .Nd:YAG lasers .

Ground state for the TiCGround state for the TiCxx--

(X) and excited vibrational (X) and excited vibrational states of the neutral TiCstates of the neutral TiCxx (A-D) were observed.(A-D) were observed.

Fundamental vibrations of Fundamental vibrations of neutral molecules neutral molecules extrapolated from excited extrapolated from excited vibrational levels.vibrational levels.

Wang, X.B; Ding, C.F; Wang, L.S; J. Phys. Chem. A 1997, 101, 7699-7701.

355 nm 532 nm

Background – PES Background – PES StudiesStudies No previous calculations No previous calculations

had been made for TiChad been made for TiC3-3-

55; prediction for their ; prediction for their structures were made by structures were made by comparing this data to comparing this data to previous YCprevious YCxx and LaC and LaCxx research.research.

Since the C-C bond is Since the C-C bond is strong and less likely to strong and less likely to break than a TiC bond, break than a TiC bond, they predicted ring-like they predicted ring-like structures for TiCstructures for TiC3-53-5, , similar to YCsimilar to YCxx and LaC and LaCxx..

TiCTiC22 560 ± 50 cm560 ± 50 cm-1-1

TiCTiC33 650 ± 30 cm650 ± 30 cm-1-1

TiCTiC44 440 ± 40 cm440 ± 40 cm-1-1

TiCTiC55 240 ± 60 cm240 ± 60 cm-1-1

Wang, X.B; Ding, C.F; Wang, L.S; J. Phys. Chem. A 1997, 101, 7699-7701.

Totally symmetric modes.

Background – PES StudyBackground – PES Study

ProblemProblem: The vibrational fundamental of : The vibrational fundamental of the neutral molecule is extrapolated from the neutral molecule is extrapolated from the higher vibrational energy levels. the higher vibrational energy levels.

The reported observations have large The reported observations have large margins of error, in the range of 30 - 60 margins of error, in the range of 30 - 60 cmcm-1-1..

Note: These are the only results available Note: These are the only results available for TiCfor TiC2-52-5 in the NIST Chemistry in the NIST Chemistry WebBook.WebBook.

Background – DFT StudyBackground – DFT Study

R. Sumathi and M. Hendrickx published a R. Sumathi and M. Hendrickx published a DFT survey of TiCDFT survey of TiCxx, x=2-4, solving , x=2-4, solving ab initioab initio the energy levels of several isomers.the energy levels of several isomers.

Vibrational frequencies for each isomer Vibrational frequencies for each isomer and electronic state were solved.and electronic state were solved.

Calculated frequencies for the optimum Calculated frequencies for the optimum isomer were in good agreement with those isomer were in good agreement with those observed by Wang, observed by Wang, et alet al..

Confirm TiCConfirm TiC22 has C has C2v2v symmetry with a symmetry with a stretching mode at 587 cmstretching mode at 587 cm-1-1. Note that . Note that Wang, Wang, et alet al. observed 560 . observed 560 ±± 50 cm 50 cm-1-1..

Background – DFT Study Background – DFT Study

Below: Optimized geometries for singlet, triplet ( ) and quintet [ ] isomers of TiC3 at the B3LYP level of theory.

Bond length in Å.

TiC3

Above: Plot of relative energies (kcal/mol) of the various isomers of TiC3 in different electronic states.

Background – DFT StudyBackground – DFT Study

TiC3 Singlet

TiC4 Triplet

Calculated Frequencies:1531.4; 1281.3; 833.6; 686.5; 591.2; 465.3 cm-1

Calculated Frequencies:1882.7; 1789.2; 1055.5; 601.1; 473.6; 472.2; 399.6; 391.1; 251.9 cm-1

Observed Frequencies (Wang):650 ±± 30 cm-1

Observed Frequencies (Wang):440 ±± 40 cm-1

Background – DFT StudyBackground – DFT Study

This study is exhaustive in This study is exhaustive in considering several possible isomers considering several possible isomers and electronic states for the chosen and electronic states for the chosen molecules.molecules.

Unfortunately, this study does not Unfortunately, this study does not provide estimated provide estimated intensitiesintensities for for these different modes of TiCthese different modes of TiC33 and and TiCTiC44..

Current Research & Current Research & ExperimentExperiment

Experimental ApparatusExperimental ApparatusNd-YAG

1064 nm pulsed laser

Quartz window

laser focusing lens

Ar

To pump10-7 Torr or better

CsI window

To pump10-3 Torr

Carbon rod

Titanium rod

gold mirror ~ 10K

Bomem DA3.16 Fourier Transform Spectrometer

• KBr beam splitter• liquid N2 cooled MCT detector (400 - 4000 cm-1)

Survey Spectrum of Ti + Survey Spectrum of Ti + 1212CC The following (best) spectra of titanium The following (best) spectra of titanium

and graphite ablation were obtained in and graphite ablation were obtained in June 2005. June 2005.

Three bands of interest appear: 624.3 Three bands of interest appear: 624.3 cmcm-1-1, 915.7 cm, 915.7 cm-1-1, 1484.1 cm, 1484.1 cm-1-1..

These three bands are from These three bands are from oneone experiment where the laser window experiment where the laser window nearly broke (hitting the C-rod). Thus, nearly broke (hitting the C-rod). Thus, less intense light was hitting the rod, less intense light was hitting the rod, and less Carbon deposited.and less Carbon deposited.

These are the strongest these bands These are the strongest these bands appeared in Ti + appeared in Ti + 1212C experiments.C experiments.

TiC CandidatesTiC Candidates

620 640

624

.3

61

6.9

910 920 930

915

.7

91

2.2

1480 1490

1484

.11

48

5.1

Experiment:90 min. deposition12C < 2.0 W; Ti~ 2.7 WAnneal 14 – 26 KSpectra at 26 K.

Experimental TechniqueExperimental Technique

Metal carbide experiments are best performed Metal carbide experiments are best performed using a dual ablation technique. This allows using a dual ablation technique. This allows more control over multiple evaporation rates more control over multiple evaporation rates than single-rod ablation.than single-rod ablation.

Baked Baked 1313C low-enrichment (l.e.) rods, though C low-enrichment (l.e.) rods, though stronger due to baking, take one month to stronger due to baking, take one month to prepare. Soft rods, which are non-baked, are prepare. Soft rods, which are non-baked, are weaker.weaker.

Experimental technique needs to be adjusted Experimental technique needs to be adjusted for limitations of the samples. Soft rods for limitations of the samples. Soft rods cannot be used at the same laser power or as cannot be used at the same laser power or as long as baked rods.long as baked rods.

Experimental TechniqueExperimental Technique

ProblemProblem: Aforementioned TiC candidates : Aforementioned TiC candidates appeared weakly using l.e. appeared weakly using l.e. 1313C rods (if at C rods (if at all!). all!).

Baked l.e. Baked l.e. 1313C rods were previously used C rods were previously used (power ~1.5 W). Signal diminishes (power ~1.5 W). Signal diminishes quickly. Too little deposition of Ti.quickly. Too little deposition of Ti.

New baked rods not readily available. New baked rods not readily available. Soft rods must be utilized.Soft rods must be utilized.

Consider reducing laser power on Consider reducing laser power on Carbon rod, in spirit of the Ti-Carbon rod, in spirit of the Ti-1212C results.C results.

Experimental TechniqueExperimental TechniqueOverall effect of reducing laser power on Carbon rod. No annealing. 1800 – 2200 cm-1. At low power. C3, C6, C9 significantly stronger. Other chains also stronger. Not correct! Weaker!

2

2.5

3

3.5

4

1800 1850 1900 1950 2000 2050 2100 2150

(Used) Baked. 10 min dep. ~1.3 Watts.

(New) Soft. 25 min dep. ~0.8 Watts.

C3

C3

C3

C9C6

C7

C7 C5

Theoretical Results for Theoretical Results for TiCTiC33

~1541 cm-1

~1506

~1530

-1

-1

1484 cmScale = 0.963

1541 cm

-1Shift(1506) 1450 cm

-1Shift(1530) 1473 cm

Scaled Values for 1484 cm-1

Experimental TechniqueExperimental Technique

1.82

1.84

1.86

1.88

1.9

1.92

1440 1460 1480 1500 1520 1540

C4

C4 (~8%)

C4

C4

1484.1

C5

C5

C5

1450.9 (~9% 1484)

1473.5*(~57% 1484)

??

?

Baseline corrected.40 min dep. 18K.

High Enrichment High Enrichment 1313C C ExperimentExperiment

1.82

1.83

1.84

1.85

1.86

1410 1420 1430 1440 1450 1460 1470 1480 1490 1500

1435.5

Baseline corrected.20 min dep. 22K.

ResultsResults TiCTiC33 with with CC2v2v symmetry may have a symmetry may have a

vibrational mode at 1484.1 cmvibrational mode at 1484.1 cm-1-1. Better . Better resolution of the shift at 1473 and high resolution of the shift at 1473 and high enrichment enrichment 1313C experiments are needed to C experiments are needed to confirm this.confirm this.

As of yet, no shifts of the 915.7 cmAs of yet, no shifts of the 915.7 cm-1-1 or or 624.3 cm624.3 cm-1-1 band have been observed. band have been observed.

Laser powers of ~0.8 W on the l.e. carbon Laser powers of ~0.8 W on the l.e. carbon rod produces small carbon chains rod produces small carbon chains abundantly. Longer carbon chains may be abundantly. Longer carbon chains may be constructed by annealing these.constructed by annealing these.

Low laser power has proven to help in Low laser power has proven to help in sharpening and obtaining shifts of small sharpening and obtaining shifts of small metal-carbides, as seen in CrCmetal-carbides, as seen in CrC3 3 (Bates).(Bates).

Further WorkFurther Work

Resolve the ‘feature’ at 1473 cmResolve the ‘feature’ at 1473 cm-1 -1 as as best as possible.best as possible.

Additional high enrichment Additional high enrichment 1313C C experiments need to be run for the experiments need to be run for the TiCTiC33 candidate. Some of these will be candidate. Some of these will be soft rods.soft rods.

Experiments to study and obtain Experiments to study and obtain shifts 624 cmshifts 624 cm-1-1 and 915 cm and 915 cm-1-1 bands bands are needed.are needed.