Anharmonic vibrational frequencies and vibrationally-averaged structures of key species in hydrocarbon combustion: HCO+, HCO, HNO, HOO, HOO-, CH3 +, and CH3

• Published in: Molecular physics Vol. 107; no. 8-12; pp. 1283 - 1301
• Main Authors: Keçeli, Murat, Shiozaki, Toru, Yagi, Kiyoshi, Hirata, So
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 20-04-2009
• Subjects: anharmonicity; electron correlation; hydrocarbon combustion; molecular vibrations; potential energy surfaces
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/00268970902889626

A general scheme to predict anharmonic vibrational frequencies and vibrationally-averaged structures and rotational constants of molecules is presented with applications to some key species in hydrocarbon combustion (some also of importance in atmospheric and/or interstellar chemistry): HCO
+
, HCO, HNO, HOO, HOO
-
,
, and CH
3
. A combination of coupled-cluster singles and doubles (CCSD), CCSD with a second-order perturbation correction in the space of triples [CCSD(2)
T
] and in the space of triples and quadruples [CCSD(2)
TQ
], and a correlation-consistent basis set series has been employed to achieve the complete-correlation, complete-basis-set limits of the potential energy surfaces (PESs) of these species near equilibrium geometries. A new, compact representation of PESs that combines two existing representations, namely, a fourth-order Taylor expansion and numerical values on a rectilinear grid, has been proposed and shown to yield accurate frequencies, when combined with vibrational general-order configuration-interaction method. The predicted frequencies (and the observed in parentheses, when available) of the fundamentals are as follows: 823 (830), 2175 (2184), and 3083 (3089) cm
−1
in HCO
+
; 1079 (1081), 1874 (1868), 2432 (2434) cm
−1
in HCO; 1503 (1501), 1572 (1565), and 2683 (2684) cm
−1
in HNO; 1121 (1098), 1399 (1392), and 3447 (3436) cm
−1
in HOO; 739, 1088, and 3587 cm
−1
in HOO
-
; 1383 (1359 ± 7), 1384 (1370 ± 7), 2940, and 3096 (3108) cm
−1
in
; 565 (606), 1377, 3002 (3004), and 3139 (3161) cm
−1
in CH
3
. The mean absolute deviation in the predicted frequencies is 11 cm
−1
.
†Dedicated to Professor Henry F. Schaefer III on the occasion of his 65th birthday.