Sean Peebles | Eastern Illinois University (original) (raw)

Papers by Sean Peebles

Proceedings of the 70th International Symposium on Molecular Spectroscopy, 2015

Advances in Quantum Chemistry

ABSTRACT

The rotational spectrum of diethylsilane has been assigned using broadband chirped-pulse Fourier-... more The rotational spectrum of diethylsilane has been assigned using broadband chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy. Previously, Fourier-transform microwave rotational spectra were observed using a Balle-Flygare type instrument for the ^{28}Si isotopologues of the gauche-gauche, trans-gauche, and trans-trans conformers. In the present study, a broadband microwave spectrum was obtained at the University of Virginia, taking advantage of the ability to perform deep signal averaging to increase the measurement sensitivity. To obtain a full structural determination of the conformers of this molecule, spectra for the ^{29}Si, ^{30}Si, and single ^{13}C substitutions for the gauche-gauche, the trans-gauche, and the trans-trans species were assigned. Substitution (r_s) structures and inertial fit (r_0) structures were determined and a comparison between the experimental and ab initio structures will be presented. For the ^{28}Si isotopologues, the percent differences between the experimental and ab initio rotational constants are less than 1.5% for the trans-trans and trans-gauche and are between 2.0 and 5.0% for the gauche-gauche conformer. The structural parameters will be compared between this molecule, diethylgermane and other silicon containing molecules and the relative abundances of the three conformers will be discussed. S.A. Peebles, M.M. Serafin, R.A. Peebles, G.A. Guirgis, and H.D. Stidham J. Phys. Chem. A, (2009), DOI: 10.1021/jp811049n.

The rotational spectrum of the CHClF 2 -H 2 O weakly bound dimer has been measured using both chi... more The rotational spectrum of the CHClF 2 -H 2 O weakly bound dimer has been measured using both chirpedpulse and resonant cavity Fourier-transform microwave spectroscopy in the 5-18 GHz range. The structure of the complex has been determined by analysis of the moments of inertia of five isotopologues of the dimer. The primary interaction between the two monomers is a weak C-HÁ Á ÁO contact (R HÁ Á ÁO = 2.332(3) Å) with a C-ClÁ Á ÁH-O contact also present (R ClÁ Á ÁH = 2.749(13) Å). The observed structure is in reasonable agreement with ab initio calculations at the MP2/6-311++G(2d,2p) level, although these predict a ClÁ Á ÁH distance that is significantly longer than the experimental results indicate. The rotational transitions of all isotopologues containing H 2 O or D 2 O were doubled, with relative intensities of the observed transitions consistent with an internal rotation of the water molecule leading to exchange of equivalent hydrogen atoms. Fitting the upper and lower components of the transitions using an effective Hamiltonian with the ERHAM program has yielded an energy difference between the tunneling states of 16.0(4) GHz, resulting in an estimate of the barrier to internal rotation of 195(5) cm À1 (to be compared with an ab initio estimate of 117cmAˋ1).Thebindingenergyofthecomplexisestimatedtobe117 cm À1 ). The binding energy of the complex is estimated to be 117cmAˋ1).Thebindingenergyofthecomplexisestimatedtobe5.5(2) kJ/mol ($460 cm À1 ) from a pseudo-diatomic approximation and assumption of a Lennard-Jones intermolecular potential.

Rotational spectra for the five naturally occurring germanium isotopologues of the anti-anti conf... more Rotational spectra for the five naturally occurring germanium isotopologues of the anti-anti conformer of n-butylgermane have been measured using a Fourier-transform microwave spectrometer operating in the 4-18 GHz range. This conformer, determined by ab initio calculations at the MP2/6-311++G(2d,2p) level to be the most stable of five possible conformers, has a heavy atom planar structure and dipole moment values (for the ^{74}Ge species) of mu_a = 0.7332(85) D and mu_b = 0.489(46) D, with mu_{ total} = 0.881(26) D. Nuclear quadrupole coupling constants have also been determined for the I = 9/2 ^{73}Ge nucleus and are in reasonable agreement with ab initio calculations. Small splittings, which were particularly apparent on the very weak b-type transitions for all isotopic species, are presumably due to rotation of one or both of the internal rotors (CH_3 and GeH_3) although these splittings have not yet been resolved sufficiently well to allow determination of any internal rotation...

Proceedings of the 70th International Symposium on Molecular Spectroscopy, 2015

The far infrared beamline of the Canadian Light Source synchrotron facility has been used to reco... more The far infrared beamline of the Canadian Light Source synchrotron facility has been used to record three rotationally resolved vibrational bands of 1,1-dichloroethylene in the 500-1000 cm-1 range, at 0.00096 cm-1 resolution. These correspond, for the H_2C=C35Cl_2 isotopologue, to an a-type band (CCl_2 antisymmetric stretch) at 796.0 cm-1, a b-type band (CCl_2 symmetric stretch) at 603.0 cm-1, and a c-type band (CH_2 wag) at 868.6 cm-1. Anharmonic frequency calculations at the MP2/6-311++G(2d,2p) level, combined with rotational and centrifugal distortion constants from a millimeter wave study of the ground state, were an invaluable aid in facilitating the spectroscopic assignment for this asymmetric top ({κ} = -0.58). Analysis of the 796 cm-1 band is nearly complete, giving well determined excited state rotational and centrifugal distortion constants. Results of this analysis and progress with analysis of the other two bands will be presented. Z. Kisiel, L. Pszczolkowski, Z. Naturfo...

C--H ... X hydrogen bonds with systematic variation of halogens (X = F, Cl, Br) have been examine... more C--H ... X hydrogen bonds with systematic variation of halogens (X = F, Cl, Br) have been examined using Fourier-Transform Microwave (FTMW) spectroscopy. Rotational constants for trifluoromethane--vinyl fluoride (TFM...VF) were consistent with a Cs symmetry structure that exhibited both bifurcated and single C--H ... F interactions between the TFM and VF. This near prolate asymmetric top exhibited three-fold internal rotation of the CF_3 group causing characteristic doubling in its spectra. Initial assignments were completed using chirped-pulse FTMW spectroscopy with additional measurements made using a resonant-cavity FTMW spectrometer. Rotational constants from ab initio calculations at the MP2/6-311++G(2d,2p) level were in agreement with preliminary experimental values (A= 4828 MHz, B = 1049 MHz, C= 1018 MHz). XIAM was used to provide the barrier to internal rotation (25(5) cm-1) and other spectral information. Spectroscopic parameters for the normal isotopic species as well as p...

The Journal of Physical Chemistry A, 2004

ABSTRACT The rotational spectra of the normal species and four isotopically substituted species o... more ABSTRACT The rotational spectra of the normal species and four isotopically substituted species of the dimethyl ether−OCS dimer have been measured by Fourier transform microwave spectroscopy, thereby allowing a structural determination of this weak complex. The normal isotopic species rotational constants are A = 4069.4106(23) MHz, B = 1431.7413(7) MHz, and C = 1074.2925(5) MHz, and the experimental dipole moment components are μa = 1.3046(28) D, μb = 0.8134(37) D, with μtotal = 1.5374(30) D. Rotational constants, dipole moment components, and planar moments are all consistent with a geometry in which the OCS molecule is located in the heavy-atom plane of dimethyl ether, making an O···CS angle of 96.5(2)°, and with an O···C separation of 2.916(3) Å. Ab initio calculations at the MP2/6-311++G(2d,2p) level reproduce the structure accurately, predicting rotational constants of A = 4065 MHz, B = 1450 MHz, and C = 1083 MHz.

The journal of physical chemistry. A, Jan 25, 2014

Rotational spectra of two different structural forms of the 1:1 weak complex between vinyl fluori... more Rotational spectra of two different structural forms of the 1:1 weak complex between vinyl fluoride (C2H3F) and carbon dioxide were measured using 480 MHz bandwidth chirped-pulse and resonant cavity Fourier-transform microwave spectroscopy in the 5-17 GHz region. Both structures have the CO2 molecule situated in the plane of the vinyl fluoride, such that the CO2 is interacting either with a CHF side or with a HC═CF edge of the vinyl fluoride subunit. Both observed structures are close to those predicted by ab initio geometry optimizations (corrected for basis set superposition error) at the MP2/6-311++G(2d,2p) level. Dipole moment measurements and structural fits, including determinations of principal axis coordinates for all three carbon atoms, confirm the geometries of the assigned species.

Journal of Molecular Structure: THEOCHEM, 2000

The normal isotopomer and three additional isotopic species of the OCS–(HCCH)2 trimer have been o... more The normal isotopomer and three additional isotopic species of the OCS–(HCCH)2 trimer have been observed by pulsed nozzle Fourier transform microwave spectroscopy. Semi-empirical modeling predicts a structure that has the two acetylene monomers aligned in a geometry between the well-known T-shaped orientation of the acetylene dimer and a parallel intermediate. Rotational constants and dipole moment measurements are consistent with this

Proceedings of the 69th International Symposium on Molecular Spectroscopy, 2014

Proceedings of the 69th International Symposium on Molecular Spectroscopy, 2014

The Journal of Physical Chemistry A, 1998

... Robb J. Wilson, † Sean A. Peebles, † Sonia Antolínez, ‡ M. Eugenia Sanz, ‡ and Robert L. Kucz... more ... Robb J. Wilson, † Sean A. Peebles, † Sonia Antolínez, ‡ M. Eugenia Sanz, ‡ and Robert L. Kuczkowski* †. ... Stark-effect splittings were observed by applying dc voltages of up to 5.0 kV of opposite polarity to two parallel steel mesh plates (about 30 cm apart). ...

A chirped-pulse Fourier-transform microwave (CP-FTMW) spectrometer based on the original Pate des... more A chirped-pulse Fourier-transform microwave (CP-FTMW) spectrometer based on the original Pate design has been constructed to allow analysis of any 480 MHz region in the 7 - 18 GHz range. A 1 mus chirped-pulse (0 - 240 MHz) from an arbitrary function generator is mixed with output from a microwave synthesizer and used to polarize a supersonic gas expansion; the

66th International …, 2011

... Authors: Elmuti, Lena F.; Obenchain, Daniel A.; Jurkowski, Don L.; Sanders, Amelia J.; Peeble... more ... Authors: Elmuti, Lena F.; Obenchain, Daniel A.; Jurkowski, Don L.; Sanders, Amelia J.; Peebles, Rebecca A.; Peebles, Sean A.; Steber, Amanda L.; Neill, Justin L.; Pate, Brooks H. Affiliation: AA(Department of Chemistry, Eastern Illinois University, 600 Lincoln Avenue, Charleston ...

The Journal of Physical Chemistry A, 2014

Rotational spectra of the normal isotopic species and three (13)C isotopologues of the 1:1 comple... more Rotational spectra of the normal isotopic species and three (13)C isotopologues of the 1:1 complex between vinyl fluoride (CH2 ═ CHF) and difluoromethane (CH2F2) have been measured using 480 MHz bandwidth chirped-pulse Fourier-transform microwave spectroscopy in the 6.5-20 GHz region. A structure for this dimer has been determined by fitting the moments of inertia of all isotopologues and confirmed by calculation of Kraitchman single isotopic substitution coordinates. The structure is consistent with that determined by ab initio geometry optimization at the MP2/6-311++G(2d,2p) level and has the difluoromethane subunit located on the CHF side of the vinyl fluoride subunit with three C-H · · · F contacts and with the hydrogen atoms of the CH2F2 straddling the vinyl fluoride symmetry plane.

The Journal of Physical Chemistry A, 2012

Molecular association and keto−enol tautomerization of β-cyclohexanedione (β-CHD) have been inves... more Molecular association and keto−enol tautomerization of β-cyclohexanedione (β-CHD) have been investigated in argon matrix and also in a thin solid film prepared by depositing pure β-CHD vapor on a cold (8 K) KBr window. Infrared spectra reveal that, in low-pressure vapor and argon matrix, the molecules are exclusively in diketo tautomeric form. The CH···O hydrogen bonded dimers of the diketo tautomer are produced by annealing the matrix at 28 K. No indication is found for keto−enol tautomerization of β-CHD in dimeric complexes in argon matrix within the temperature range of 8−28 K. On the other hand, in thin film of pure diketo tautomer, the conversion initiates only when the film is heated at temperatures above 165 K. The observed threshold appears to be associated with excitation of the intermolecular modes, and the IR spectra recorded at high temperatures display narrowing of vibrational bandwidths, which has been associated with reorientations of the molecules in the film. The nonoccurrence of tautomerization of the matrix isolated dimer is consistent with the barrier predicted by electronic structure calculations at B3LYP/6-311++G** and MP2/6-311++G** levels of theory. The transition state calculation predicts that CH···O interaction has a dramatic effect on lowering of the tautomerization barrier, from more than 60 kcal/mol for the bare molecule to ∼35−45 kcal/mol for dimers.

Proceedings of the 70th International Symposium on Molecular Spectroscopy, 2015

Advances in Quantum Chemistry

ABSTRACT

The rotational spectrum of diethylsilane has been assigned using broadband chirped-pulse Fourier-... more The rotational spectrum of diethylsilane has been assigned using broadband chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy. Previously, Fourier-transform microwave rotational spectra were observed using a Balle-Flygare type instrument for the ^{28}Si isotopologues of the gauche-gauche, trans-gauche, and trans-trans conformers. In the present study, a broadband microwave spectrum was obtained at the University of Virginia, taking advantage of the ability to perform deep signal averaging to increase the measurement sensitivity. To obtain a full structural determination of the conformers of this molecule, spectra for the ^{29}Si, ^{30}Si, and single ^{13}C substitutions for the gauche-gauche, the trans-gauche, and the trans-trans species were assigned. Substitution (r_s) structures and inertial fit (r_0) structures were determined and a comparison between the experimental and ab initio structures will be presented. For the ^{28}Si isotopologues, the percent differences between the experimental and ab initio rotational constants are less than 1.5% for the trans-trans and trans-gauche and are between 2.0 and 5.0% for the gauche-gauche conformer. The structural parameters will be compared between this molecule, diethylgermane and other silicon containing molecules and the relative abundances of the three conformers will be discussed. S.A. Peebles, M.M. Serafin, R.A. Peebles, G.A. Guirgis, and H.D. Stidham J. Phys. Chem. A, (2009), DOI: 10.1021/jp811049n.

The rotational spectrum of the CHClF 2 -H 2 O weakly bound dimer has been measured using both chi... more The rotational spectrum of the CHClF 2 -H 2 O weakly bound dimer has been measured using both chirpedpulse and resonant cavity Fourier-transform microwave spectroscopy in the 5-18 GHz range. The structure of the complex has been determined by analysis of the moments of inertia of five isotopologues of the dimer. The primary interaction between the two monomers is a weak C-HÁ Á ÁO contact (R HÁ Á ÁO = 2.332(3) Å) with a C-ClÁ Á ÁH-O contact also present (R ClÁ Á ÁH = 2.749(13) Å). The observed structure is in reasonable agreement with ab initio calculations at the MP2/6-311++G(2d,2p) level, although these predict a ClÁ Á ÁH distance that is significantly longer than the experimental results indicate. The rotational transitions of all isotopologues containing H 2 O or D 2 O were doubled, with relative intensities of the observed transitions consistent with an internal rotation of the water molecule leading to exchange of equivalent hydrogen atoms. Fitting the upper and lower components of the transitions using an effective Hamiltonian with the ERHAM program has yielded an energy difference between the tunneling states of 16.0(4) GHz, resulting in an estimate of the barrier to internal rotation of 195(5) cm À1 (to be compared with an ab initio estimate of 117cmAˋ1).Thebindingenergyofthecomplexisestimatedtobe117 cm À1 ). The binding energy of the complex is estimated to be 117cmAˋ1).Thebindingenergyofthecomplexisestimatedtobe5.5(2) kJ/mol ($460 cm À1 ) from a pseudo-diatomic approximation and assumption of a Lennard-Jones intermolecular potential.

Rotational spectra for the five naturally occurring germanium isotopologues of the anti-anti conf... more Rotational spectra for the five naturally occurring germanium isotopologues of the anti-anti conformer of n-butylgermane have been measured using a Fourier-transform microwave spectrometer operating in the 4-18 GHz range. This conformer, determined by ab initio calculations at the MP2/6-311++G(2d,2p) level to be the most stable of five possible conformers, has a heavy atom planar structure and dipole moment values (for the ^{74}Ge species) of mu_a = 0.7332(85) D and mu_b = 0.489(46) D, with mu_{ total} = 0.881(26) D. Nuclear quadrupole coupling constants have also been determined for the I = 9/2 ^{73}Ge nucleus and are in reasonable agreement with ab initio calculations. Small splittings, which were particularly apparent on the very weak b-type transitions for all isotopic species, are presumably due to rotation of one or both of the internal rotors (CH_3 and GeH_3) although these splittings have not yet been resolved sufficiently well to allow determination of any internal rotation...

Proceedings of the 70th International Symposium on Molecular Spectroscopy, 2015

The far infrared beamline of the Canadian Light Source synchrotron facility has been used to reco... more The far infrared beamline of the Canadian Light Source synchrotron facility has been used to record three rotationally resolved vibrational bands of 1,1-dichloroethylene in the 500-1000 cm-1 range, at 0.00096 cm-1 resolution. These correspond, for the H_2C=C35Cl_2 isotopologue, to an a-type band (CCl_2 antisymmetric stretch) at 796.0 cm-1, a b-type band (CCl_2 symmetric stretch) at 603.0 cm-1, and a c-type band (CH_2 wag) at 868.6 cm-1. Anharmonic frequency calculations at the MP2/6-311++G(2d,2p) level, combined with rotational and centrifugal distortion constants from a millimeter wave study of the ground state, were an invaluable aid in facilitating the spectroscopic assignment for this asymmetric top ({κ} = -0.58). Analysis of the 796 cm-1 band is nearly complete, giving well determined excited state rotational and centrifugal distortion constants. Results of this analysis and progress with analysis of the other two bands will be presented. Z. Kisiel, L. Pszczolkowski, Z. Naturfo...

C--H ... X hydrogen bonds with systematic variation of halogens (X = F, Cl, Br) have been examine... more C--H ... X hydrogen bonds with systematic variation of halogens (X = F, Cl, Br) have been examined using Fourier-Transform Microwave (FTMW) spectroscopy. Rotational constants for trifluoromethane--vinyl fluoride (TFM...VF) were consistent with a Cs symmetry structure that exhibited both bifurcated and single C--H ... F interactions between the TFM and VF. This near prolate asymmetric top exhibited three-fold internal rotation of the CF_3 group causing characteristic doubling in its spectra. Initial assignments were completed using chirped-pulse FTMW spectroscopy with additional measurements made using a resonant-cavity FTMW spectrometer. Rotational constants from ab initio calculations at the MP2/6-311++G(2d,2p) level were in agreement with preliminary experimental values (A= 4828 MHz, B = 1049 MHz, C= 1018 MHz). XIAM was used to provide the barrier to internal rotation (25(5) cm-1) and other spectral information. Spectroscopic parameters for the normal isotopic species as well as p...

The Journal of Physical Chemistry A, 2004

ABSTRACT The rotational spectra of the normal species and four isotopically substituted species o... more ABSTRACT The rotational spectra of the normal species and four isotopically substituted species of the dimethyl ether−OCS dimer have been measured by Fourier transform microwave spectroscopy, thereby allowing a structural determination of this weak complex. The normal isotopic species rotational constants are A = 4069.4106(23) MHz, B = 1431.7413(7) MHz, and C = 1074.2925(5) MHz, and the experimental dipole moment components are μa = 1.3046(28) D, μb = 0.8134(37) D, with μtotal = 1.5374(30) D. Rotational constants, dipole moment components, and planar moments are all consistent with a geometry in which the OCS molecule is located in the heavy-atom plane of dimethyl ether, making an O···CS angle of 96.5(2)°, and with an O···C separation of 2.916(3) Å. Ab initio calculations at the MP2/6-311++G(2d,2p) level reproduce the structure accurately, predicting rotational constants of A = 4065 MHz, B = 1450 MHz, and C = 1083 MHz.

The journal of physical chemistry. A, Jan 25, 2014

Rotational spectra of two different structural forms of the 1:1 weak complex between vinyl fluori... more Rotational spectra of two different structural forms of the 1:1 weak complex between vinyl fluoride (C2H3F) and carbon dioxide were measured using 480 MHz bandwidth chirped-pulse and resonant cavity Fourier-transform microwave spectroscopy in the 5-17 GHz region. Both structures have the CO2 molecule situated in the plane of the vinyl fluoride, such that the CO2 is interacting either with a CHF side or with a HC═CF edge of the vinyl fluoride subunit. Both observed structures are close to those predicted by ab initio geometry optimizations (corrected for basis set superposition error) at the MP2/6-311++G(2d,2p) level. Dipole moment measurements and structural fits, including determinations of principal axis coordinates for all three carbon atoms, confirm the geometries of the assigned species.

Journal of Molecular Structure: THEOCHEM, 2000

The normal isotopomer and three additional isotopic species of the OCS–(HCCH)2 trimer have been o... more The normal isotopomer and three additional isotopic species of the OCS–(HCCH)2 trimer have been observed by pulsed nozzle Fourier transform microwave spectroscopy. Semi-empirical modeling predicts a structure that has the two acetylene monomers aligned in a geometry between the well-known T-shaped orientation of the acetylene dimer and a parallel intermediate. Rotational constants and dipole moment measurements are consistent with this

Proceedings of the 69th International Symposium on Molecular Spectroscopy, 2014

Proceedings of the 69th International Symposium on Molecular Spectroscopy, 2014

The Journal of Physical Chemistry A, 1998

... Robb J. Wilson, † Sean A. Peebles, † Sonia Antolínez, ‡ M. Eugenia Sanz, ‡ and Robert L. Kucz... more ... Robb J. Wilson, † Sean A. Peebles, † Sonia Antolínez, ‡ M. Eugenia Sanz, ‡ and Robert L. Kuczkowski* †. ... Stark-effect splittings were observed by applying dc voltages of up to 5.0 kV of opposite polarity to two parallel steel mesh plates (about 30 cm apart). ...

A chirped-pulse Fourier-transform microwave (CP-FTMW) spectrometer based on the original Pate des... more A chirped-pulse Fourier-transform microwave (CP-FTMW) spectrometer based on the original Pate design has been constructed to allow analysis of any 480 MHz region in the 7 - 18 GHz range. A 1 mus chirped-pulse (0 - 240 MHz) from an arbitrary function generator is mixed with output from a microwave synthesizer and used to polarize a supersonic gas expansion; the

66th International …, 2011

... Authors: Elmuti, Lena F.; Obenchain, Daniel A.; Jurkowski, Don L.; Sanders, Amelia J.; Peeble... more ... Authors: Elmuti, Lena F.; Obenchain, Daniel A.; Jurkowski, Don L.; Sanders, Amelia J.; Peebles, Rebecca A.; Peebles, Sean A.; Steber, Amanda L.; Neill, Justin L.; Pate, Brooks H. Affiliation: AA(Department of Chemistry, Eastern Illinois University, 600 Lincoln Avenue, Charleston ...

The Journal of Physical Chemistry A, 2014

Rotational spectra of the normal isotopic species and three (13)C isotopologues of the 1:1 comple... more Rotational spectra of the normal isotopic species and three (13)C isotopologues of the 1:1 complex between vinyl fluoride (CH2 ═ CHF) and difluoromethane (CH2F2) have been measured using 480 MHz bandwidth chirped-pulse Fourier-transform microwave spectroscopy in the 6.5-20 GHz region. A structure for this dimer has been determined by fitting the moments of inertia of all isotopologues and confirmed by calculation of Kraitchman single isotopic substitution coordinates. The structure is consistent with that determined by ab initio geometry optimization at the MP2/6-311++G(2d,2p) level and has the difluoromethane subunit located on the CHF side of the vinyl fluoride subunit with three C-H · · · F contacts and with the hydrogen atoms of the CH2F2 straddling the vinyl fluoride symmetry plane.

The Journal of Physical Chemistry A, 2012

Molecular association and keto−enol tautomerization of β-cyclohexanedione (β-CHD) have been inves... more Molecular association and keto−enol tautomerization of β-cyclohexanedione (β-CHD) have been investigated in argon matrix and also in a thin solid film prepared by depositing pure β-CHD vapor on a cold (8 K) KBr window. Infrared spectra reveal that, in low-pressure vapor and argon matrix, the molecules are exclusively in diketo tautomeric form. The CH···O hydrogen bonded dimers of the diketo tautomer are produced by annealing the matrix at 28 K. No indication is found for keto−enol tautomerization of β-CHD in dimeric complexes in argon matrix within the temperature range of 8−28 K. On the other hand, in thin film of pure diketo tautomer, the conversion initiates only when the film is heated at temperatures above 165 K. The observed threshold appears to be associated with excitation of the intermolecular modes, and the IR spectra recorded at high temperatures display narrowing of vibrational bandwidths, which has been associated with reorientations of the molecules in the film. The nonoccurrence of tautomerization of the matrix isolated dimer is consistent with the barrier predicted by electronic structure calculations at B3LYP/6-311++G** and MP2/6-311++G** levels of theory. The transition state calculation predicts that CH···O interaction has a dramatic effect on lowering of the tautomerization barrier, from more than 60 kcal/mol for the bare molecule to ∼35−45 kcal/mol for dimers.