Xinchuan Huang - Academia.edu (original) (raw)

Papers by Xinchuan Huang

Research paper thumbnail of Empirical infrared line lists for five SO2 isotopologues: 32/33/34/36S16O2 and 32S18O2

Journal of Molecular Spectroscopy, 2015

ABSTRACT Using the latest published, empirically refined potential energy surface (PES) Ames-1 an... more ABSTRACT Using the latest published, empirically refined potential energy surface (PES) Ames-1 and purely ab initio CCSD(T)/aug-cc-pV(Q+d)Z dipole moment surface (DMS), we have computed infrared line lists for five symmetric isotopologues of sulfur dioxide: 32S16O2 (626), 33S16O2 (636), 34S16O2 (646), 36S16O2 (666), and 32S18O2 (828). The line lists are based on J = 0–80 rovibrational variational calculations with E′ ⩽ 8000 cm−1. The 34S16O2 and 33S16O2 line lists are compared to the experiment-based models in the HIgh-resolution TRANsmission molecular absorption database (HITRAN2012, http://www.cfa.harvard.edu/hitran/) and the Cologne Database for Molecular Spectroscopy, CDMS (http://www.astro.uni-koeln.de/cdms/). The accuracy for computed 646 band origins is similar to what has been reported for the main isotopologue, i.e. 0.01–0.03 cm−1 for bands up to 5500 cm−1. For rovibrational transitions, the 646 line position and intensity deviation patterns are much simpler and more self-consistent than those of the main isotopologue 626. The discrepancies are mainly found for higher Ka/J transitions. 626 and 646 exhibit comparable line position and intensity agreement for lower Ka/J transitions. The line position deviations for the 636 purely rotational band are parallel to those of 626 and 646, while its line intensity deviations do not show branching patterns as we found in the 626 and 646 cases. Predictions for the other minor isotopologues are expected to exhibit similar accuracy. These line lists are accurate enough to provide alternatives for missing bands of 626 and the minor isotopologues. It may significantly facilitate the laboratory spectroscopic measurement and analysis, as well as to identify these isotopologues in various astrophysical environments.

Research paper thumbnail of Linear transformation of anharmonic molecular force constants between normal and Cartesian coordinates

The Journal of Chemical Physics, 2015

A full derivation of the analytic transformation of the quadratic, cubic, and quartic force const... more A full derivation of the analytic transformation of the quadratic, cubic, and quartic force constants from normal coordinates to Cartesian coordinates is given. Previous attempts at this transformation have resulted in non-linear transformations; however, for the first time, a simple linear transformation is presented here. Two different approaches have been formulated and implemented, one of which does not require prior knowledge of the translation-rotation eigenvectors from diagonalization of the Hessian matrix. The validity of this method is tested using two molecules H2O and c-C3H2D(+).

Research paper thumbnail of Ab initio potential energy and dipole moment surfaces for H5O2 +

The Journal of chemical physics, Jan 22, 2005

Full-dimensional ab initio potential energy surface (PES) and dipole moment surface (DMS) are rep... more Full-dimensional ab initio potential energy surface (PES) and dipole moment surface (DMS) are reported for H(5)O(2) (+). Tens of thousands of coupled-cluster [CCSD(T)] and second-order Moller-Plesset (MP2) calculations of electronic energies, using aug-cc-pVTZ basis, were done. The energies were fit very precisely in terms of all the internuclear distances, using standard least-square procedures, however, with a fitting basis that satisfies permutational symmetry with respect to like atoms. The H(5)O(2) (+) PES is a fit to 48 189 CCSD(T) energies, containing 7962 polynomial coefficients. The PES has a rms fitting error of 34.9 cm(-1) for the entire data set up to 110 000 cm(-1). This surface can describe various internal floppy motions, including the H atom exchanges, monomer inversions, and monomer torsions. First- and higher-order saddle points have been located on the surface and compared with available previous theoretical work. In addition, the PES dissociates correctly (and sy...

Research paper thumbnail of Quantum calculations of vibrational energies of H3O2- on an ab initio potential

Journal of the American Chemical Society, Jan 28, 2004

We report a full-dimensional potential energy surface for H3O2-, based on fitting 66,965 ab initi... more We report a full-dimensional potential energy surface for H3O2-, based on fitting 66,965 ab initio electronic energies. A major feature of this potential is a barrier of roughly 200 cm-1 to internal rotation of the two hydroxyl groups about a line connecting the two oxygen atoms and the bridging hydrogen atom. The potential is used in calculations of vibrational energies, performed with the "Reaction Path" version of the code "MULTIMODE". The results are compared to recent infrared messenger experiments and are used to propose interpretations of the experimental results.

Research paper thumbnail of Quantum IR line list of NH3 and isotopologues for ISM and dwarf studies

Proceedings of the International Astronomical Union, 2012

ABSTRACT

Research paper thumbnail of An approach to include the effects of diffuse functions in potential energy surface calculations

The journal of physical chemistry. A, Jan 29, 2009

A new approach is proposed and investigated for approximately including the effects of diffuse fu... more A new approach is proposed and investigated for approximately including the effects of diffuse functions in one-particle basis sets when high accuracy is desired. The method is cost-effective for use in computing quartic force fields (QFFs), global potential energy surfaces (PESs), or other situations when a large part of the PES is needed. It is conservatively estimated that the use of this approximation leads to a computational savings of a factor of five, and it is argued that this could be significantly larger if input/output wait times are considered. It can be used when extrapolation to the one-particle basis set limit is performed, or it can be used simply to approximate the effect of diffuse functions for a larger basis set. The new approach is based on scaling the diffuse function effect for a smaller basis set to approximate the effect for a larger basis or an extrapolated energy in which larger basis set(s) are used. The scale factor is written as a function of the geomet...

Research paper thumbnail of Comparison of one-particle basis set extrapolation to explicitly correlated methods for the calculation of accurate quartic force fields, vibrational frequencies, and spectroscopic constants: application to H2O, N2H+, NO2+, and C2H2

The Journal of chemical physics, Jan 28, 2010

One-particle basis set extrapolation is compared with one of the new R12 methods for computing hi... more One-particle basis set extrapolation is compared with one of the new R12 methods for computing highly accurate quartic force fields (QFFs) and spectroscopic data, including molecular structures, rotational constants, and vibrational frequencies for the H(2)O, N(2)H(+), NO(2)(+), and C(2)H(2) molecules. In general, agreement between the spectroscopic data computed from the best R12 and basis set extrapolation methods is very good with the exception of a few parameters for N(2)H(+) where it is concluded that basis set extrapolation is still preferred. The differences for H(2)O and NO(2)(+) are small and it is concluded that the QFFs from both approaches are more or less equivalent in accuracy. For C(2)H(2), however, a known one-particle basis set deficiency for C-C multiple bonds significantly degrades the quality of results obtained from basis set extrapolation and in this case the R12 approach is clearly preferred over one-particle basis set extrapolation. The R12 approach used in t...

Research paper thumbnail of Dipole surface and infrared intensities for the cis- and trans-HOCO and DOCO radicals

The journal of physical chemistry. A, Jan 15, 2013

The vibrational spectra for the HOCO radical in both of its conformers and deuterated isotopologu... more The vibrational spectra for the HOCO radical in both of its conformers and deuterated isotopologues are shown here for the first time. Building on previous work with coupled cluster quartic force fields (QFFs) in the computation of the fundamental vibrational frequencies for both cis- and trans-HOCO, coupled cluster dipole surfaces are now provided for both HOCO conformers and their corresponding deuterated isotopologues. These surfaces and subsequent vibrational configuration interaction (VCI) computations produce the intensities of transitions into vibrational states including the fundamentals, overtones, and first few combination bands of less than 4000 cm(-1), slightly beyond the O-H stretch. Simulated spectra with an artificial full width at half-maximum broadening of 10 cm(-1) are also provided in order to aid in the characterization of HOCO's vibrational frequencies and to assist detection in various laboratory or astronomical observations.

Research paper thumbnail of Anharmonic rovibrational calculations of singlet cyclic C4 using a new ab initio potential and a quartic force field

The Journal of chemical physics, Jan 14, 2013

We report a CCSD(T)/cc-pCV5Z quartic force field (QFF) and a semi-global CCSD(T)-F12b/aug-cc-pVTZ... more We report a CCSD(T)/cc-pCV5Z quartic force field (QFF) and a semi-global CCSD(T)-F12b/aug-cc-pVTZ potential energy surface (PES) for singlet, cyclic C4. Vibrational fundamentals, combinations, and overtones are obtained using vibrational second-order perturbation theory (VPT2) and the vibrational configuration-interaction (VCI) approach. Agreement is within 10 cm(-1) between the VCI calculated fundamentals on the QFF and PES using the MULTIMODE (MM) program, and VPT2 and VCI results agree for the fundamentals. The agreement between VPT2-QFF and MM-QFF results is also good for the C4 combinations and overtones. The J = 1 and J = 2 rovibrational energies are reported from both VCI (MM) on the PES and VPT2 on the QFF calculations. The spectroscopic constants of (12)C4 and two C2v-symmetry, single (13)C-substituted isotopologues are presented, which may help identification of cyclic C4 in future experimental analyses or astronomical observations.

Research paper thumbnail of Highly accurate potential energy surface, dipole moment surface, rovibrational energy levels, and infrared line list for ³²S¹⁶O₂ up to 8000 cm⁻¹

The Journal of chemical physics, Jan 21, 2014

A purely ab initio potential energy surface (PES) was refined with selected (32)S(16)O2 HITRAN da... more A purely ab initio potential energy surface (PES) was refined with selected (32)S(16)O2 HITRAN data. Compared to HITRAN, the root-mean-squares error (σ(RMS)) for all J = 0-80 rovibrational energy levels computed on the refined PES (denoted Ames-1) is 0.013 cm(-1). Combined with a CCSD(T)/aug-cc-pV(Q+d)Z dipole moment surface (DMS), an infrared (IR) line list (denoted Ames-296K) has been computed at 296 K and covers up to 8000 cm(-1). Compared to the HITRAN and CDMS databases, the intensity agreement for most vibrational bands is better than 85%-90%. Our predictions for (34)S(16)O2 band origins, higher energy (32)S(16)O2 band origins and missing (32)S(16)O2 IR bands have been verified by most recent experiments and available HITRAN data. We conclude that the Ames-1 PES is able to predict (32/34)S(16)O2 band origins below 5500 cm(-1) with 0.01-0.03 cm(-1) uncertainties, and the Ames-296K line list provides continuous, reliable and accurate IR simulations. The K(a)-dependence of both l...

Research paper thumbnail of High accuracy potential energy and dipole moment surfaces for water clusters

Research paper thumbnail of Vibrational levels of methanol, calculated by MULTIMODE for a Reaction Path deter-mined from an accurate ab initio potential energy surface in full dimensionality

Research paper thumbnail of Quantum calculations of vibrational energies of H3O2 (-) and H5O2 (+) with new ab initio potentials

We report a full-dimensional potential energy surface for H3O2-, based on fitting 66,965 ab initi... more We report a full-dimensional potential energy surface for H3O2-, based on fitting 66,965 ab initio electronic energies. A major feature of this potential is a barrier of roughly 200 cm-1 to internal rotation of the two hydroxyl groups about a line connecting the two oxygen atoms and the bridging hydrogen atom. The potential is used in calculations of vibrational energies, performed with the "Reaction Path" version of the code "MULTIMODE". The results are compared to recent infrared messenger experiments and are used to propose interpretations of the experimental results.

Research paper thumbnail of THE MULTIMODE APPROACH TO CHALLENGING PROBLEMS IN VIBRATION SPECTROSCOPY

The 'Multimode' Approach to Challenging Problems in Vibrational Spectro... more The 'Multimode' Approach to Challenging Problems in Vibrational Spectroscopy. Joel M. Bowman, Stuart Carter, Xinchuan Huang. ... “RVIB3” (Carter-Handy), “RVIB4” (CH-Colwell), “DVR3D” (Tennyson), see CCP6, Carrington, Guo, Bowman, Leforstier, Light, etc. ...

Research paper thumbnail of SPECTROSCOPIC SIGNATURES OF LARGE AMPLITUDE VIBRATIONAL MOTIONS IN H $ _5 $ O $ _2^+ $ AND H $ _3 $ O $ _2^-$

Research paper thumbnail of Computational chemistry with" MULTIMODE" and new strategies for ab initio potential energy surface

Research paper thumbnail of Computing the Temperature Dependent Rovibrational Spectrum of Ammonia

Molecules with large amplitude motions possess significant complexity in their rovibrational and ... more Molecules with large amplitude motions possess significant complexity in their rovibrational and purely rotational spectra. Because of this complexity, they are ideal molecules to be used to characterize the physical conditions of the celestial objects and galactic environments in which they are observed, which was noted more than two decades ago by Ho and Townes. The simplest and best characterized molecule with a large amplitude motion of interest in astronomy is ammonia. The available experimental data for even this molecule, however, is not sufficient to generate a synthetic spectrum that compares well with observations from the Spitzer Space Telescope of one of the coolest known T dwarfs Gl570D, and this is likely to be the case for any celestial environments above 400K. The IRS instrument on the Spitzer Space Telescope has already recorded spectra that cannot be well modeled and interpreted using the available experimental data for ammonia. In response to the urgent need for better line lists, including intensities, we propose to use the tools of theoretical spectroscopy, combined with refinement using the available experimental data, to obtain highly accurate line lists for ammonia and its isotopomers. Through the use of high accuracy electronic structure calculations, and refinement of the resulting potential energy surface (PES) with the available experimental data, Schwenke has already constructed highly accurate lists for all isotopomers of the water molecule. The accuracy of the resulting PES, transition energies, and intensities has been demonstrated by later spectroscopic studies. We propose to use a similar approach for ammonia. Our approach will be to use high-level electronic structure calculations to construct a highly accurate, isotope independent PES and dipole surface for the ammonia molecule. The resulting highly accurate PESs and dipole moment surfaces will then be used to solve the nuclear Schroedinger equation to generate the necessary line lists.

Research paper thumbnail of COMP 169-Highly accurate ab initio quartic force fields of C3H+ and HO2+

Research paper thumbnail of THEORETICAL ROVIBRATIONAL SPECTRA FOR MOLECULES CONTAINING A LARGE-AMPLITUDE MOTION: AMMONIA

Research paper thumbnail of PHYS 705-Calculation of highly accurate rovibrational spectra for molecules containing a large-amplitude motion: Ammonia

Research paper thumbnail of Empirical infrared line lists for five SO2 isotopologues: 32/33/34/36S16O2 and 32S18O2

Journal of Molecular Spectroscopy, 2015

ABSTRACT Using the latest published, empirically refined potential energy surface (PES) Ames-1 an... more ABSTRACT Using the latest published, empirically refined potential energy surface (PES) Ames-1 and purely ab initio CCSD(T)/aug-cc-pV(Q+d)Z dipole moment surface (DMS), we have computed infrared line lists for five symmetric isotopologues of sulfur dioxide: 32S16O2 (626), 33S16O2 (636), 34S16O2 (646), 36S16O2 (666), and 32S18O2 (828). The line lists are based on J = 0–80 rovibrational variational calculations with E′ ⩽ 8000 cm−1. The 34S16O2 and 33S16O2 line lists are compared to the experiment-based models in the HIgh-resolution TRANsmission molecular absorption database (HITRAN2012, http://www.cfa.harvard.edu/hitran/) and the Cologne Database for Molecular Spectroscopy, CDMS (http://www.astro.uni-koeln.de/cdms/). The accuracy for computed 646 band origins is similar to what has been reported for the main isotopologue, i.e. 0.01–0.03 cm−1 for bands up to 5500 cm−1. For rovibrational transitions, the 646 line position and intensity deviation patterns are much simpler and more self-consistent than those of the main isotopologue 626. The discrepancies are mainly found for higher Ka/J transitions. 626 and 646 exhibit comparable line position and intensity agreement for lower Ka/J transitions. The line position deviations for the 636 purely rotational band are parallel to those of 626 and 646, while its line intensity deviations do not show branching patterns as we found in the 626 and 646 cases. Predictions for the other minor isotopologues are expected to exhibit similar accuracy. These line lists are accurate enough to provide alternatives for missing bands of 626 and the minor isotopologues. It may significantly facilitate the laboratory spectroscopic measurement and analysis, as well as to identify these isotopologues in various astrophysical environments.

Research paper thumbnail of Linear transformation of anharmonic molecular force constants between normal and Cartesian coordinates

The Journal of Chemical Physics, 2015

A full derivation of the analytic transformation of the quadratic, cubic, and quartic force const... more A full derivation of the analytic transformation of the quadratic, cubic, and quartic force constants from normal coordinates to Cartesian coordinates is given. Previous attempts at this transformation have resulted in non-linear transformations; however, for the first time, a simple linear transformation is presented here. Two different approaches have been formulated and implemented, one of which does not require prior knowledge of the translation-rotation eigenvectors from diagonalization of the Hessian matrix. The validity of this method is tested using two molecules H2O and c-C3H2D(+).

Research paper thumbnail of Ab initio potential energy and dipole moment surfaces for H5O2 +

The Journal of chemical physics, Jan 22, 2005

Full-dimensional ab initio potential energy surface (PES) and dipole moment surface (DMS) are rep... more Full-dimensional ab initio potential energy surface (PES) and dipole moment surface (DMS) are reported for H(5)O(2) (+). Tens of thousands of coupled-cluster [CCSD(T)] and second-order Moller-Plesset (MP2) calculations of electronic energies, using aug-cc-pVTZ basis, were done. The energies were fit very precisely in terms of all the internuclear distances, using standard least-square procedures, however, with a fitting basis that satisfies permutational symmetry with respect to like atoms. The H(5)O(2) (+) PES is a fit to 48 189 CCSD(T) energies, containing 7962 polynomial coefficients. The PES has a rms fitting error of 34.9 cm(-1) for the entire data set up to 110 000 cm(-1). This surface can describe various internal floppy motions, including the H atom exchanges, monomer inversions, and monomer torsions. First- and higher-order saddle points have been located on the surface and compared with available previous theoretical work. In addition, the PES dissociates correctly (and sy...

Research paper thumbnail of Quantum calculations of vibrational energies of H3O2- on an ab initio potential

Journal of the American Chemical Society, Jan 28, 2004

We report a full-dimensional potential energy surface for H3O2-, based on fitting 66,965 ab initi... more We report a full-dimensional potential energy surface for H3O2-, based on fitting 66,965 ab initio electronic energies. A major feature of this potential is a barrier of roughly 200 cm-1 to internal rotation of the two hydroxyl groups about a line connecting the two oxygen atoms and the bridging hydrogen atom. The potential is used in calculations of vibrational energies, performed with the "Reaction Path" version of the code "MULTIMODE". The results are compared to recent infrared messenger experiments and are used to propose interpretations of the experimental results.

Research paper thumbnail of Quantum IR line list of NH3 and isotopologues for ISM and dwarf studies

Proceedings of the International Astronomical Union, 2012

ABSTRACT

Research paper thumbnail of An approach to include the effects of diffuse functions in potential energy surface calculations

The journal of physical chemistry. A, Jan 29, 2009

A new approach is proposed and investigated for approximately including the effects of diffuse fu... more A new approach is proposed and investigated for approximately including the effects of diffuse functions in one-particle basis sets when high accuracy is desired. The method is cost-effective for use in computing quartic force fields (QFFs), global potential energy surfaces (PESs), or other situations when a large part of the PES is needed. It is conservatively estimated that the use of this approximation leads to a computational savings of a factor of five, and it is argued that this could be significantly larger if input/output wait times are considered. It can be used when extrapolation to the one-particle basis set limit is performed, or it can be used simply to approximate the effect of diffuse functions for a larger basis set. The new approach is based on scaling the diffuse function effect for a smaller basis set to approximate the effect for a larger basis or an extrapolated energy in which larger basis set(s) are used. The scale factor is written as a function of the geomet...

Research paper thumbnail of Comparison of one-particle basis set extrapolation to explicitly correlated methods for the calculation of accurate quartic force fields, vibrational frequencies, and spectroscopic constants: application to H2O, N2H+, NO2+, and C2H2

The Journal of chemical physics, Jan 28, 2010

One-particle basis set extrapolation is compared with one of the new R12 methods for computing hi... more One-particle basis set extrapolation is compared with one of the new R12 methods for computing highly accurate quartic force fields (QFFs) and spectroscopic data, including molecular structures, rotational constants, and vibrational frequencies for the H(2)O, N(2)H(+), NO(2)(+), and C(2)H(2) molecules. In general, agreement between the spectroscopic data computed from the best R12 and basis set extrapolation methods is very good with the exception of a few parameters for N(2)H(+) where it is concluded that basis set extrapolation is still preferred. The differences for H(2)O and NO(2)(+) are small and it is concluded that the QFFs from both approaches are more or less equivalent in accuracy. For C(2)H(2), however, a known one-particle basis set deficiency for C-C multiple bonds significantly degrades the quality of results obtained from basis set extrapolation and in this case the R12 approach is clearly preferred over one-particle basis set extrapolation. The R12 approach used in t...

Research paper thumbnail of Dipole surface and infrared intensities for the cis- and trans-HOCO and DOCO radicals

The journal of physical chemistry. A, Jan 15, 2013

The vibrational spectra for the HOCO radical in both of its conformers and deuterated isotopologu... more The vibrational spectra for the HOCO radical in both of its conformers and deuterated isotopologues are shown here for the first time. Building on previous work with coupled cluster quartic force fields (QFFs) in the computation of the fundamental vibrational frequencies for both cis- and trans-HOCO, coupled cluster dipole surfaces are now provided for both HOCO conformers and their corresponding deuterated isotopologues. These surfaces and subsequent vibrational configuration interaction (VCI) computations produce the intensities of transitions into vibrational states including the fundamentals, overtones, and first few combination bands of less than 4000 cm(-1), slightly beyond the O-H stretch. Simulated spectra with an artificial full width at half-maximum broadening of 10 cm(-1) are also provided in order to aid in the characterization of HOCO's vibrational frequencies and to assist detection in various laboratory or astronomical observations.

Research paper thumbnail of Anharmonic rovibrational calculations of singlet cyclic C4 using a new ab initio potential and a quartic force field

The Journal of chemical physics, Jan 14, 2013

We report a CCSD(T)/cc-pCV5Z quartic force field (QFF) and a semi-global CCSD(T)-F12b/aug-cc-pVTZ... more We report a CCSD(T)/cc-pCV5Z quartic force field (QFF) and a semi-global CCSD(T)-F12b/aug-cc-pVTZ potential energy surface (PES) for singlet, cyclic C4. Vibrational fundamentals, combinations, and overtones are obtained using vibrational second-order perturbation theory (VPT2) and the vibrational configuration-interaction (VCI) approach. Agreement is within 10 cm(-1) between the VCI calculated fundamentals on the QFF and PES using the MULTIMODE (MM) program, and VPT2 and VCI results agree for the fundamentals. The agreement between VPT2-QFF and MM-QFF results is also good for the C4 combinations and overtones. The J = 1 and J = 2 rovibrational energies are reported from both VCI (MM) on the PES and VPT2 on the QFF calculations. The spectroscopic constants of (12)C4 and two C2v-symmetry, single (13)C-substituted isotopologues are presented, which may help identification of cyclic C4 in future experimental analyses or astronomical observations.

Research paper thumbnail of Highly accurate potential energy surface, dipole moment surface, rovibrational energy levels, and infrared line list for ³²S¹⁶O₂ up to 8000 cm⁻¹

The Journal of chemical physics, Jan 21, 2014

A purely ab initio potential energy surface (PES) was refined with selected (32)S(16)O2 HITRAN da... more A purely ab initio potential energy surface (PES) was refined with selected (32)S(16)O2 HITRAN data. Compared to HITRAN, the root-mean-squares error (σ(RMS)) for all J = 0-80 rovibrational energy levels computed on the refined PES (denoted Ames-1) is 0.013 cm(-1). Combined with a CCSD(T)/aug-cc-pV(Q+d)Z dipole moment surface (DMS), an infrared (IR) line list (denoted Ames-296K) has been computed at 296 K and covers up to 8000 cm(-1). Compared to the HITRAN and CDMS databases, the intensity agreement for most vibrational bands is better than 85%-90%. Our predictions for (34)S(16)O2 band origins, higher energy (32)S(16)O2 band origins and missing (32)S(16)O2 IR bands have been verified by most recent experiments and available HITRAN data. We conclude that the Ames-1 PES is able to predict (32/34)S(16)O2 band origins below 5500 cm(-1) with 0.01-0.03 cm(-1) uncertainties, and the Ames-296K line list provides continuous, reliable and accurate IR simulations. The K(a)-dependence of both l...

Research paper thumbnail of High accuracy potential energy and dipole moment surfaces for water clusters

Research paper thumbnail of Vibrational levels of methanol, calculated by MULTIMODE for a Reaction Path deter-mined from an accurate ab initio potential energy surface in full dimensionality

Research paper thumbnail of Quantum calculations of vibrational energies of H3O2 (-) and H5O2 (+) with new ab initio potentials

We report a full-dimensional potential energy surface for H3O2-, based on fitting 66,965 ab initi... more We report a full-dimensional potential energy surface for H3O2-, based on fitting 66,965 ab initio electronic energies. A major feature of this potential is a barrier of roughly 200 cm-1 to internal rotation of the two hydroxyl groups about a line connecting the two oxygen atoms and the bridging hydrogen atom. The potential is used in calculations of vibrational energies, performed with the "Reaction Path" version of the code "MULTIMODE". The results are compared to recent infrared messenger experiments and are used to propose interpretations of the experimental results.

Research paper thumbnail of THE MULTIMODE APPROACH TO CHALLENGING PROBLEMS IN VIBRATION SPECTROSCOPY

The 'Multimode' Approach to Challenging Problems in Vibrational Spectro... more The 'Multimode' Approach to Challenging Problems in Vibrational Spectroscopy. Joel M. Bowman, Stuart Carter, Xinchuan Huang. ... “RVIB3” (Carter-Handy), “RVIB4” (CH-Colwell), “DVR3D” (Tennyson), see CCP6, Carrington, Guo, Bowman, Leforstier, Light, etc. ...

Research paper thumbnail of SPECTROSCOPIC SIGNATURES OF LARGE AMPLITUDE VIBRATIONAL MOTIONS IN H $ _5 $ O $ _2^+ $ AND H $ _3 $ O $ _2^-$

Research paper thumbnail of Computational chemistry with" MULTIMODE" and new strategies for ab initio potential energy surface

Research paper thumbnail of Computing the Temperature Dependent Rovibrational Spectrum of Ammonia

Molecules with large amplitude motions possess significant complexity in their rovibrational and ... more Molecules with large amplitude motions possess significant complexity in their rovibrational and purely rotational spectra. Because of this complexity, they are ideal molecules to be used to characterize the physical conditions of the celestial objects and galactic environments in which they are observed, which was noted more than two decades ago by Ho and Townes. The simplest and best characterized molecule with a large amplitude motion of interest in astronomy is ammonia. The available experimental data for even this molecule, however, is not sufficient to generate a synthetic spectrum that compares well with observations from the Spitzer Space Telescope of one of the coolest known T dwarfs Gl570D, and this is likely to be the case for any celestial environments above 400K. The IRS instrument on the Spitzer Space Telescope has already recorded spectra that cannot be well modeled and interpreted using the available experimental data for ammonia. In response to the urgent need for better line lists, including intensities, we propose to use the tools of theoretical spectroscopy, combined with refinement using the available experimental data, to obtain highly accurate line lists for ammonia and its isotopomers. Through the use of high accuracy electronic structure calculations, and refinement of the resulting potential energy surface (PES) with the available experimental data, Schwenke has already constructed highly accurate lists for all isotopomers of the water molecule. The accuracy of the resulting PES, transition energies, and intensities has been demonstrated by later spectroscopic studies. We propose to use a similar approach for ammonia. Our approach will be to use high-level electronic structure calculations to construct a highly accurate, isotope independent PES and dipole surface for the ammonia molecule. The resulting highly accurate PESs and dipole moment surfaces will then be used to solve the nuclear Schroedinger equation to generate the necessary line lists.

Research paper thumbnail of COMP 169-Highly accurate ab initio quartic force fields of C3H+ and HO2+

Research paper thumbnail of THEORETICAL ROVIBRATIONAL SPECTRA FOR MOLECULES CONTAINING A LARGE-AMPLITUDE MOTION: AMMONIA

Research paper thumbnail of PHYS 705-Calculation of highly accurate rovibrational spectra for molecules containing a large-amplitude motion: Ammonia