New ab initio potential energy surfaces (PESs) for the two lowest-lying singlet ′ and ′′ electronic states of CH2, coupled by the Renner-Teller (RT) effect and meant for the spectroscopic study, are presented. The surfaces are constructed using a dual-level strategy. The internally contracted multireference configuration interaction calculations with the Davidson correction, using the aug-cc-pVQZ basis set, are employed to obtain 3042 points at the lower level. The core and core-valence correlation effects are taken into account in the ab initio calculations with a modified optimized aug-cc-pCVQZ basis set for the higher-level points. The analytical representations of these PESs, with the inclusion of the nonadiabatic RT terms, are obtained by the nonlinear least-squares fit of the calculated points to three-body expansion. Quantum dynamical calculations are performed on these PESs, and the computed vibronic energy levels for the two singlet electronic states are in excellent agreement with experiment. 1. Introduction The CH2 biradical has been the subject of many theoretical and experimental studies, due to its distinct electronic characteristics and chemical and physical properties. It is the direct chemical precursor of the widely observed CH radical [1]. As a crucial link in the photodissociation sequence of cometary methane, CH2 plays a significant role in the chemistry of hydrocarbon combustion and the astrophysics of interstellar medium [2–5]. Since Herzberg and Johns [2] carried out a detailed analysis of the high-resolution absorption spectrum of the singlet CH2 in the near ultraviolet region half a century ago, several groups [6–11] have observed the direct absorption spectra or subsequent monitoring of fluorescence via laser-induced fluorescence, stimulated emission pumping, dispersed fluorescence, and so forth. Experimental investigations of the spectroscopy provided abundant and precise rovibronic energy levels [12–16]. Recently, bands in the CH2 - transition between 12500 and 13000？cm？1 were recorded at Doppler-limited resolution utilizing a transient frequency-modulation (FM) laser absorption spectrometer by Chang and coworkers [16]. An unexpected and particularly complicated rovibronic structure was detected for and vibronic levels. Comparison of the calculated spectra on the available potential energy surfaces (PESs) [17–19] with the experimental spectra of Herzberg and Johns [2] indicates that the labeling of some vibrational levels is quite inconsistent, which can be ascribed to the local perturbations from the vibrational resonances
References
[1]
R. A. Be？rda, M. C. Van Hemert, and E. F. Van Dishoeck, “Photodissociation of CH2. I. Potential energy surfaces of the dissociation into CH and H,” The Journal of Chemical Physics, vol. 97, no. 11, pp. 8240–8249, 1992.
[2]
G. Herzberg and J. W. C. Johns, “The Spectrum and Structure of Singlet CH2,” Proceedings of the Royal Society of London A, vol. 295, no. 1441, pp. 107–128, 1966.
[3]
A. Kalemos, T. H. Dunning, A. Mavridis, and J. F. Harrison, “CH2 revisited,” Canadian Journal of Chemistry, vol. 82, no. 6, pp. 684–693, 2004.
[4]
C. D. Sherrill, M. L. Leininger, T. J. V. Huis, and H. F. Schaefer III, “Structures and vibrational frequencies in the full configuration interaction limit: predictions for four electronic states of methylene using a triple-zeta plus double polarization (TZ2P) basis,” The Journal of Chemical Physics, vol. 108, no. 3, pp. 1040–1049, 1998.
[5]
M. N. R. Ashfold, M. A. Fullstone, G. Hancock, and G. Duxbury, “Laser induced fluorescence spectroscopy of the CD2 ( ) radical: Renner-teller effect in CH2 and CD2,” Molecular Physics, vol. 45, no. 4, pp. 887–896, 1982.
[6]
W. Xie, C. Harkin, H. L. Dai, W. H. Green, Q. K. Zheng, and A. J. Mahoney, “Transient vibrational spectroscopy of CH2 v2 = 2,” Journal of Molecular Spectroscopy, vol. 138, no. 2, pp. 596–601, 1989.
[7]
W. Xie, C. Harkin, and H. L. Dai, “Bending overtones and barrier height of CH2 by flash photolysis stimulated emission pumping,” The Journal of Chemical Physics, vol. 93, no. 7, pp. 4615–4623, 1990.
[8]
G. V. Hartland, D. Qin, and H. L. Dai, “Renner-Teller effect on the highly excited bending levels of CH2,” The Journal of Chemical Physics, vol. 102, no. 17, pp. 6641–6645, 1995.
[9]
B. C. Chang, M. Wu, G. E. Hall, and T. J. Sears, “Near-infrared vibronic spectrum of the CH2 ← transition,” The Journal of Chemical Physics, vol. 101, no. 11, pp. 9236–9245, 1994.
[10]
K. Kobayashi, L. D. Pride, and T. J. Sears, “Absorption spectroscopy of singlet CH2 near 9500 ,” The Journal of Physical Chemistry A, vol. 104, no. 45, pp. 10119–10124, 2000.
[11]
H. Petek, D. J. Nesbitt, D. C. Darwin, P. R. Ogilby, C. B. Moore, and D. A. Ramsay, “Analysis of CH2 (1,0,0) and (0,0,1) Coriolis-coupled states, - spin-orbit coupling, and the equilibrium structure of CH2 ,” The Journal of Chemical Physics, vol. 91, no. 11, pp. 6566–6578, 1989.
[12]
G. E. Hall, A. V. Komissarov, and T. J. Sears, “Doppler-resolved spectroscopy as an assignment tool in the spectrum of singlet methylene,” The Journal of Physical Chemistry A, vol. 108, no. 39, pp. 7922–7927, 2004.
[13]
A. J. Marr, T. J. Sears, and B. C. Chang, “Near-infrared spectroscopy of CH2 by frequency modulated diode laser absorption,” The Journal of Chemical Physics, vol. 109, no. 9, pp. 3431–3442, 1998.
[14]
Z. Wang, Y. Kim, G. E. Hall, and T. J. Sears, “State mixing and predissociation in the ← band system of singlet methylene studied by optical-optical double resonance,” The Journal of Physical Chemistry A, vol. 112, no. 39, pp. 9248–9254, 2008.
[15]
K. Kobayashi, G. E. Hall, and T. J. Sears, “The spectrum of CH2 near 1.36 and 0.92？μm: reevaluation of rotational level structure and perturbations in (010),” The Journal of Chemical Physics, vol. 124, no. 18, Article ID 184320, 2006.
[16]
C. -H. Chang, Z. Wang, G. E. Hall, T. J. Sears, and J. Xin, “Transient laser absorption spectroscopy of CH2 near 780？nm,” Journal of Molecular Spectroscopy, vol. 267, no. 1-2, pp. 50–57, 2011.
[17]
W. H. Green Jr., N. C. Handy, P. J. Knowles, and S. Carter, “Theoretical assignment of the visible spectrum of singlet methylene,” The Journal of Chemical Physics, vol. 94, no. 1, pp. 118–132, 1991.
[18]
G. Duxbury, A. Alijah, B. D. McDonald, and C. Jungen, “Stretch-bender calculations of the effects of orbital angular momentum and vibrational resonances in the spectrum of singlet methylene,” The Journal of Chemical Physics, vol. 108, no. 6, pp. 2351–2360, 1998.
[19]
J. P. Gu, G. Hirsch, R. J. Buenker et al., “A theoretical study of the absorption spectrum of singlet CH2,” Journal of Molecular Structure, vol. 517-518, pp. 247–264, 2000.
[20]
R. Renner, “Zur Theorie der Wechselwirkung zwischen Elektronen- und Kernbewegung bei dreiatomigen, stabf？rmigen Molekülen,” Zeitschrift für Physik, vol. 92, no. 3-4, pp. 172–193, 1934.
[21]
G. J. Halasz, A. Vibok, R. Baer, and M. Baer, “Renner-Teller nonadiabatic coupling terms: an ab-initio study of the HNH molecule,” The Journal of Chemical Physics, vol. 124, no. 8, Article ID 081106, 4 pages, 2006.
[22]
G. J. Halász, á. Vibók, R. Baer, and M. Baer, “D matrix analysis of the Renner-Teller effect: an accurate three-state diabatization for NH2,” The Journal of Chemical Physics, vol. 125, no. 9, Article ID 094102, 9 pages, 2006.
[23]
S. Zhou, Z. Li, D. Xie, S. Y. Lin, and H. Guo, “An ab initio global potential-energy surface for NH2 (A2A′) and vibrational spectrum of the Renner-TellerA2A′-X2A′′ system,” The Journal of Chemical Physics, vol. 130, no. 18, Article ID 184307, 10 pages, 2009.
[24]
G. Duxbury, B. D. McDonald, M. Van Gogh, A. Alijah, C. Jungen, and H. Palivan, “The effects of vibrational resonances on Renner-Teller coupling in triatomic molecules: the stretch-bender approach,” The Journal of Chemical Physics, vol. 108, no. 6, pp. 2336–2350, 1998.
[25]
C. Jungen, D. N. Malm, and A. J. Merer, “Analysis of a transition of CS2 in the near ultraviolet,” Canadian Journal of Physics, vol. 51, no. 14, pp. 1471–1490, 1973.
[26]
B. Ostoji？, “The dissociation of singlet methylene,” Journal of Molecular Spectroscopy, vol. 212, no. 1, pp. 130–131, 2002.
[27]
B. Bussery-Honvault, P. Honvault, and J. M. Launay, “A study of the → reaction: global potential energy surface and quantum dynamics,” The Journal of Chemical Physics, vol. 115, no. 23, pp. 10701–10708, 2001.
[28]
L. Ba？ares, F. J. Aoiz, P. Honvault, B. Bussery-Honvault, and J. M. Launay, “Quantum mechanical and quasi-classical trajectory study of the reaction dynamics,” The Journal of Chemical Physics, vol. 118, no. 2, pp. 565–568, 2003.
[29]
B. Bussery-Honvault, J. Julien, P. Honvault, and J.-M. Launay, “Global 1 1A″ potential energy surface of CH2 and quantum dynamics of a sideways insertion mechanism for the → reaction,” Physical Chemistry Chemical Physics, vol. 7, no. 7, pp. 1476–1481, 2005.
[30]
S. Joseph and J. C. Varandas, “Accurate double many-body expansion potential energy surface for the lowest singlet state of methylene,” The Journal of Physical Chemistry A, vol. 113, no. 16, pp. 4175–4183, 2009.
[31]
A. J. C. Varandas, “Intermolecular and intramolecular potentials: topographical aspects, calculation, and functional representation via a double many-body expansion method,” Advances in Chemical Physics, vol. 74, pp. 255–338, 1988.
[32]
S. Joseph, P. J. S. B. Caridade, and A. J. C. Varandas, “Quasiclassical trajectory study of the reaction and isotopomeric variants: kinetic isotope effect and cd/ch branching ratio,” The Journal of Physical Chemistry A, vol. 115, no. 27, pp. 7882–7890, 2011.
[33]
R. Dawes, A. F. Wagner, and D. L. Thompson, “Ab initio wavenumber accurate spectroscopy: and HCN vibrational levels on automatically generated IMLS potential energy surfaces,” The Journal of Physical Chemistry A, vol. 113, no. 16, pp. 4709–4721, 2009.
[34]
X. Liu, W. Bian, X. Zhao, and X. Tao, “Potential energy surface intersections in the reactive system,” The Journal of Chemical Physics, vol. 125, Article ID 074306, 7 pages, 2006.
[35]
H. Zhao, W. Bian, and K. Liu, “A theoretical study of the reaction of O(3P) with isobutene,” Journal of Physical Chemistry A, vol. 110, no. 25, pp. 7858–7866, 2006.
[36]
N. Matsunaga and D. R. Yarkony, “Energies and derivative couplings in the vicinity of a conical intersection. II. CH2(23A′′,333A′′) and H2S( A′′ A′′), unexpected results in an ostensibly standard case,” The Journal of Chemical Physics, vol. 107, no. 19, pp. 7825–7838, 1997.
[37]
D. R. Yarkony, “Diabolical conical intersections,” Reviews of Modern Physics, vol. 68, no. 4, pp. 985–1013, 1996.
[38]
J. Ivanic, G. J. Atchity, and K. Ruedenberg, “Violation of the weak noncrossing rule between totally symmetric closed-shell states in the valence-isoelectronic series O3, S3, SO2, and S2O,” The Journal of Chemical Physics, vol. 107, no. 11, pp. 4307–4317, 1997.
[39]
G. J. Atchity and K. Ruedenberg, “Strong shifts in diabatic nondynamic electron correlations cause conical intersection between low-lying closed-shell adiabatic singlets of like symmetry in ozone,” The Journal of Chemical Physics, vol. 99, no. 5, pp. 3790–3798, 1993.
[40]
H. Ma, X. Liu, W. Bian, L. Meng, and S. Zheng, “A theoretical study of the mechanism and kinetics of reactions,” ChemPhysChem, vol. 7, no. 8, pp. 1786–1794, 2006.
[41]
P. Jensen, M. Brumm, W. P. Kraemer, and P. R. Bunker, “A treatment of the Renner effect using the MORBID hamiltonian,” Journal of Molecular Spectroscopy, vol. 171, no. 1, pp. 31–57, 1995.
[42]
K. A. Peterson and T. H. Dunning, “Accurate correlation consistent basis sets for molecular core-valence correlation effects: the second row atoms Al-Ar, and the first row atoms B-Ne revisited,” The Journal of Chemical Physics, vol. 117, no. 23, pp. 10548–10560, 2002.
[43]
J. Cao, Z. Zhang, C. Zhang, W. Bian, and Y. Guo, “Kinetic study on the H+SiH4 abstraction reaction using an ab initio potential energy surface,” The Journal of Chemical Physics, vol. 134, no. 2, 2011.
[44]
H. J. Werner and P. J. Knowles, “A second order multiconfiguration SCF procedure with optimum convergence,” The Journal of Chemical Physics, vol. 82, no. 11, pp. 5053–5063, 1985.
[45]
H. J. Werner and W. Meyer, “A quadratically convergent multiconfiguration-self-consistent field method with simultaneous optimization of orbitals and Cl coefficients,” The Journal of Chemical Physics, vol. 73, no. 5, pp. 2342–2356, 1980.
[46]
H. J. Werner and W. Meyer, “A quadratically convergent MCSCF method for the simultaneous optimization of several states,” The Journal of Chemical Physics, vol. 74, no. 10, pp. 5794–5801, 1981.
[47]
H. J. Werner and P. J. Knowles, “An efficient internally contracted multiconfiguration-reference configuration interaction method,” The Journal of Chemical Physics, vol. 89, no. 9, pp. 5803–5814, 1988.
[48]
D. E. Woon and T. H. Dunning, “Gaussian basis sets for use in correlated molecular calculations. V. Core-valence basis sets for boron through neon,” The Journal of Chemical Physics, vol. 103, no. 11, pp. 4572–4585, 1995.
[49]
A. K. Wilson, T. Van Mourik, and T. H. Dunning, “Gaussian basis sets for use in correlated molecular calculations. VI. Sextuple zeta correlation consistent basis sets for boron through neon,” Journal of Molecular Structure: THEOCHEM, vol. 388, no. 1–3, pp. 339–349, 1996.
[50]
H. Partridge and D. W. Schwenke, “The determination of an accurate isotope dependent potential energy surface for water from extensive ab initio calculations and experimental data,” The Journal of Chemical Physics, vol. 106, no. 11, pp. 4618–4639, 1997.
[51]
O. L. Polyansky, A. G. Császár, S. V. Shirin et al., “High-accuracy ab initio rotation-vibration transitions for water,” Science, vol. 299, no. 5606, pp. 539–542, 2003.
[52]
Z. Zhang, H. Ma, and W. Bian, “Accurate quantum mechanical study of the Renner-Teller effect in the singlet CH2,” The Journal of Chemical Physics, vol. 135, Article ID 154303, 10 pages, 2011.
[53]
H.-J. Werner, P. J. Knowles, R. Lindh, et al., MOLPRO, version 2006.1, a package of ab initio programs.
[54]
W. Bian and H.-J. Werner, “Global ab initio potential energy surfaces for the CIH2 reactive system,” The Journal of Chemical Physics, vol. 112, no. 1, pp. 220–229, 2000.
[55]
J. R. Flores and R. J. Gdanitz, “Accurately solving the electronic Schr？dinger equation of small atoms and molecules using explicitly correlated (r12-)MR-CI. VIII. Valence excited states of methylene (CH2),” The Journal of Chemical Physics, vol. 123, no. 14, Article ID 144316, 8 pages, 2005.
[56]
G. Duxbury and C. Jungen, “Effects of orbital angular momentum in CH2 The Renner-Teller effect,” Journal of Polymer Science B, vol. 63, no. 6, pp. 981–998, 1988.
[57]
D. C. Comeau, I. Shavitt, P. Jensen, and P. R. Bunker, “An ab initio determination of the potential-energy surfaces and rotation-vibration energy levels of methylene in the lowest triplet and singlet states and the singlet—triplet splitting,” The Journal of Chemical Physics, vol. 90, no. 11, pp. 6491–6500, 1989.
[58]
H. Petek, D. J. Nesbitt, D. C. Darwin, and C. Bradley Moore, “Visible absorption and magnetic‐rotation spectroscopy of 1CH2: The analysis of the state,” The Journal of Chemical Physics, vol. 86, no. 3, pp. 1172–1188, 1987.
[59]
G. V. Hartland, D. Qin, and H. L. Dai, “Fourier transform dispersed fluorescence spectroscopy: observation of new vibrational levels in the 5000–8000？ region of CH2,” The Journal of Chemical Physics, vol. 98, no. 3, pp. 2469–2472, 1993.
[60]
W. H. Green, I. C. Chen, H. Bitto, D. R. Guyer, and C. B. Moore, “New vibrational bands of CH2 ( ),” Journal of Molecular Spectroscopy, vol. 138, no. 2, pp. 614–629, 1989.
[61]
L. J. Doriol, F. Gatti, C. Iung, and H. D. Meyer, “Computation of vibrational energy levels and eigenstates of fluoroform using the multiconfiguration time-dependent Hartree method,” The Journal of Chemical Physics, vol. 129, no. 22, Article ID 224109, 9 pages, 2008.
[62]
H. D. Meyer, F. L. Quéré, C. Léonard, and F. Gatti, “Calculation and selective population of vibrational levels with the Multiconfiguration Time-Dependent Hartree (MCTDH) algorithm,” Chemical Physics, vol. 329, no. 1-3, pp. 179–192, 2006.
[63]
H.-D. Meyer, U. Manthe, and L. S. Cederbaum, “The multi-configurational time-dependent Hartree approach,” Chemical Physics Letters, vol. 165, no. 1, pp. 73–78, 1990.
[64]
M. H. Beck, A. J？ckle, G. A. Worth, and H. D. Meyer, “The multiconfiguration time-dependent Hartree (MCTDH) method: a highly efficient algorithm for propagating wavepackets,” Physics Report, vol. 324, no. 1, pp. 1–105, 2000.
[65]
G. A. Worth, M. H. Beck, A. J？ckle, and H.-D. Meyer, The MCTDH Package, Version 8.2, 2000, University of Heidelberg, Germany. H.-D. Meyer, Version 8.3, 2002, Version 8.4, 2007, http://mctdh.uni-hd.de.
