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Jay C. Amicangelo, Ian Campbell, and Joshua Wilkins
Evidence of Internal Rotation in the O-H Stretching Region of the 1:1 Methanol-Benzene Complex in an Argon matrix Jay C. Amicangelo, Ian Campbell, and Joshua Wilkins
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CH3OH-C6H6 Complex 1:1 H- complex observed in low temperature argon matrix 2013 ISMS TE08 CH3OH O–H stretch (1) 20 K Deposition 1:1:1600 CH3OH:C6H6:Ar 8 hours complex peaks CH3OH:C6H6:Ar CH3OH:Ar C6H6:Ar MP2/aug-cc-pVDZ 16.0 kJ/mol 2.42 Å
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CH3OH/Ar + C6H6/Ar Isotopic Spectra
CH3OH/CD3OD O–H(D) stretch regions (1) CH3OH:C6H6:Ar CH3OH:Ar C6H6:Ar CH3OH : C6H6 CD3OD : C6H6 complex peaks complex peaks CH3OH : C6D6 CD3OD : C6D6 complex peaks complex peaks
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Multiple Peaks in Matrix Isolation Spectra
Matrix site splitting Anneal matrix or vary sample/matrix ratio Molecular aggregation Vary sample/matrix ratio Distinct complex geometries Vary matrix temperature Rotational structure Vary matrix temperature
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Matrix Isolation Infrared Spectroscopy Experiments
Co-depositions in Ar: CH3OH + C6H6 & CD3OD + C6H6 20 K deposition; 4 – 6 mmol/hr; hours; 0.5 cm-1 resolution Concentration study: 1: :1600 S:M ratios Annealing: 20 K → 35 K Vary matrix temperature: 20 K ↔ 8 K C6H6:Ar CH3OH:Ar
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20 K Deposition Spectra CH3OH/CD3OD O–H(D) stretch regions (1)
O–H stretch 1:800 CH3OH:Ar + 1:800 C6H6:Ar primary peak: cm-1 secondary peak: cm-1 = 4.0 cm-1 primary secondary CH3OH:C6H6:Ar CH3OH:Ar C6H6:Ar O–D stretch 1:600 CD3OD:Ar + 1:600 C6H6:Ar primary peak: cm-1 secondary peak: cm-1 = 3.3 cm-1 primary secondary CD3OD:C6H6:Ar CD3OD:Ar C6H6:Ar
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Spectra normalized to 3615.8 cm-1 peak
CH3OH:Ar + C6H6:Ar Concentration Study 1:200 – 1:1600 S:M ratios Spectra normalized to cm-1 peak O–H stretch region (1) primary secondary 1:200 1:400 1:800 1:1000 1:1600 Suggests secondary peak not due to aggregation both peaks due to 1:1 complex
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Deposition + Annealing Spectra
20 K deposit → 35 K anneal (15 min) → 20 K spectrum O–H stretch (1) 1:800 CH3OH:Ar + 1:800 C6H6:Ar higher complex primary secondary 35 K 20 K O–D stretch (1) 1:600 CD3OD:Ar + 1:600 C6H6:Ar higher complex primary 35 K secondary 20 K Suggests secondary peaks not due to matrix site splitting
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1:1 complex O–H stretch (1)
CH3OH:Ar + C6H6:Ar Matrix Temperature Variation 1:400 S:M ratios; 20 K → 8 K matrix temperature 1:1 complex O–H stretch (1) primary peak decreases & splits 20 K matrix 8 K matrix secondary peak shifts & increases Suggests multiple peaks not due to distinct complex geometries
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H2O-C6F6 Complexes in N2 matrix
J. Phys. Chem. A 2013, 117, 1336 H2O 2 region Monomer H2O:C6F6:N2 1 2 3 H2O:C6F6:N2 H2O:N2 C6F6:N2 17 K 8 K 1 2 3
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1:1 complex O–D stretch (1)
CD3OD:Ar + C6H6:Ar Matrix Temperature Variation 1:400 S:M ratios; 20 K → 8 K matrix temperature 1:1 complex O–D stretch (1) primary peak decreases 20 K matrix 8 K matrix secondary peak shifts & increases Intensity changes consistent with CH3OH-C6H6 spectra
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1:1 complex O–H stretch (1)
CH3OH:Ar + C6H6:Ar Matrix Temperature Variation 1:400 S:M ratios; 20 K → 8 K → 20 K → 8 K → 20 K 1:1 complex O–H stretch (1) Intensity changes are reversible suggests “rotational” structure 20 K matrix 8 K matrix 20 K matrix 8 K matrix primary peak secondary peak 20 K matrix
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1:1 complex O–D stretch (1)
CD3OD:Ar + C6H6:Ar Matrix Temperature Variation 1:400 S:M ratios; 20 K → 8 K → 20 K → 8 K → 20 K 1:1 complex O–D stretch (1) Intensity changes are reversible suggests “rotational” structure 20 K matrix 8 K matrix 20 K matrix 8 K matrix primary peak secondary peak 20 K matrix
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CH3OH Internal Rotation in Ne and p-H2
Splittings observed for isolated CH3OH attributed to internal rotation about C–O bond (A/E tunneling splitting) 1:3000 CH3OH:p-H2; 7 region Y. P. Lee: Science 2006, 311, 365 1:20000 CH3OH:Ne; 1 region J. P. Perchard: Chem. Phys. 2007, 332, 86 AA AE EE EA 3.5 K dark H2O vapor 5 K anneal 3.5 K dep Spectra and data for 1 region not reported AE & AA transitions with T EE & EA transitions with T
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CH3OH-C6H6 Internal Rotation Calculations
Rigid potential energy scans; MP2/aug-cc-pVDZ opt values Suggests internal CH3OH rotation opt value
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20 K → 8 K matrix temperature
CH3OH:Ar + C6H6:Ar Matrix Spectra 1:800 S:M ratios; C6H6 C–H OOP bend region (CH) 1:800 CH3OH:Ar + 1:800 C6H6:Ar 20 K deposition & spectra complex peaks CH3OH:C6H6:Ar C6H6:Ar CH3OH:Ar 1:800 CH3OH:Ar + 1:800 C6H6:Ar 20 K → 8 K matrix temperature 20 K matrix complex peaks 8 K matrix
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Summary Concentration study Matrix annealing (35 K)
Suggests secondary peak not aggregation Matrix annealing (35 K) Suggests secondary peak not matrix site splitting Matrix temperature variation (20 K → 8 K) Suggests “rotational” structure and not distinct complex geometries CH3OH-C6H6 internal rotation calculations Suggests internal CH3OH rotation
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H2O O–H stretching region (1 & 3)
H2O:Ar Matrix Temperature Variation 1:1000 S:M ratio; 20 K → 8 K → 20 K → 8 K → 20 K H2O O–H stretching region (1 & 3) 000101 101000 101202 110111 111110 000111 101110 20 K 8 K 20 K Intensities of most transitions increase with T decrease 8 K 20 K
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CH3OH/Ar + C6H6/Ar Isotopic Spectra
C6H6/C6D6 OOP bend regions CH3OH:C6H6:Ar C6H6:Ar CH3OH:Ar CH3OH : C6H6 CD3OD : C6H6 complex peaks complex peaks CH3OH : C6D6 CD3OD : C6D6 complex peak complex peak
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