Department of Chemistry, Washington State University, Pullman, Washington 99164, USA.
J Chem Phys. 2011 Feb 28;134(8):084308. doi: 10.1063/1.3556990.
A composite coupled cluster methodology is used with systematic sequences of correlation consistent basis sets to accurately determine the structure, vibrational frequencies, and isotopic shifts for trans-HNNO ((2)A'), cis-HNNO ((2)A'), and ONHN ((2)A'). Anharmonic corrections to the vibrational frequencies and rotational constants are obtained using density functional theory. With basis sets larger than double-zeta, large differences between restricted open-shell Hartree-Fock (ROHF)-based and unrestricted Hartree-Fock (UHF)-based coupled cluster harmonic frequencies are calculated, with the UHF-based ones judged to be more reliable based on an analysis of the orbital hessian eigenvalues. The final calculated anharmonic vibrational band origins are generally in good agreement with the experimental values measured in rare gas matrices. The calculation of the vibrational band origins of the isovalent NO(2) molecule at similar levels of theory exhibits an agreement with experiment to within a few wavenumbers. In the latter case, however, a ROHF treatment was required since the UHF approach failed to provide realistic frequencies for the antisymmetric stretching mode. The heat of formation at 0 K of trans-HNNO is calculated to be 50.5 ± 0.5 kcal∕mol using a very similar composite coupled cluster methodology as in the structure and harmonic frequency determinations.
采用复合耦合簇方法，并结合系统的相关一致基集序列，准确地确定了反式-HNNO((2)A')、顺式-HNNO((2)A')和 ONHN((2)A')的结构、振动频率和同位素位移。使用密度泛函理论获得了振动频率和转动常数的非谐校正。在双ζ以上的基集上，基于受限开壳 Hartree-Fock（ROHF）和非受限 Hartree-Fock（UHF）的耦合簇谐波频率之间存在很大差异，基于轨道 Hessian 本征值的分析，UHF 基的被判断为更可靠。最终计算的非谐振动带起源通常与稀有气体基质中测量的实验值吻合良好。在类似理论水平上计算等电子 NO(2)分子的振动带起源时，实验值的一致性在几个波数内。然而，在后一种情况下，由于 UHF 方法未能为反对称伸缩模式提供现实的频率，因此需要 ROHF 处理。使用与结构和谐波频率确定非常相似的复合耦合簇方法，计算反式-HNNO 的 0 K 生成热为 50.5±0.5 kcal/mol。
