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1、CH351LDryLab3/p.3UsingSPARTANtosolvetheQuantumMechanicsofMolecules:InternuclearPotentials,Vibrations,IRSpectra,andEquilibriumGeometriesIntroductionToday,computationalchemistrysoftwareiswidelyavailableascommercialproductsthatcanberunonapersonalcomputer.Graphicaluserinterfacesallo
2、wforsimpleinputtingofmolecularstructures,andthesolutionofthequantummechanicalproperties(energies,reactivities,dipolemoments,spectra,etc.)ofarangeofmoleculesbecomespracticalforgeneraluse.Unfortunately,duetotheavailabilityofthissoftwareanditseaseofuse,thereistoolittleemphasisgiven
3、tounderstandingthelimitationsofthesoftware.Inthislab,wewillusethesoftwarepackagecalledSPARTANandexploretheeffectofchangingbasesontheinteratomicpotentialfunction.Theobjectivesofthislaboratoryassignmentaretogiveyousomeexperiencewiththesedifferentlevelsandapplicationsofcomputationa
4、lchemistry.WewillfirstperformanabinitiocalculationoftheinteratomicpotentialofHClandcompareittothatderivedfromthespectroscopicmeasurementsyoumadelasttime.QuantumMechanicalVibrationsandInfraredSpectroscopyInfrared(IR)spectroscopyisoneofthemostusefultoolsinorganicchemistryforidenti
5、ficationofmolecularstructure.Somemolecularvibrationalmotionsarecharacteristicofonlyonebondorbondingenvironment(C-Haliphatic,C-Haromatic,C-N,carbonyl,etc.)orforgroupsofatoms.Thefrequenciesofthesevibrationscanthusoftenbeusedforstructuralelucidationandfunctionalgroupidentification.
6、Othermolecularvibrationalfrequenciesinvolvemovementofalmostalloftheatomsinthemolecule,hencethefrequenciesofthesevibrationsarecharacteristicofthemoleculeasawhole.Thesevibrationalfrequenciesaregenerallyreferredtoasbeinginthe‘fingerprint’region(wavenumbersfrom1500cm-1to400cm-1).Inf
7、ormationfromthefingerprintregionisusefulinmakingadirectcomparisonofanIRspectrumforanunknownsampletolibraryorreferencespectraforpurposesofmolecularspeciation.Usingquantummechanics,itispossibletocalculatethevibrationalfrequenciesassociatedwithIRspectra.Thenucleiareassumedtomovemuc
8、hmoreslowlythantheelectrons,whicharemuchlighter