NaC分子基态及其低电子激发态

Ground and Low-Lying Excited States of NaC Molecule

运用包含Davidson修正的多参考组态相互作用(MRCI+Q)方法结合6-311++G(3df,3pd)基组计算了NaC分子基态(X4Σ)以及三个低电子激发态(a2Π,b2Σ,A4Π)的势能曲线(PECs),确定出相应态的平衡键长Re和垂直激发能Te.然后将PECs拟合到Murrel-Sorbie(MS)解析势能函数形式,继而获得各态的光谱数据:谐振频率ωe、离解能De、非谐性常数ωeχe、转动常数Be、Drot和振转耦合常数αe.计算结果表明:X4Σ、a2Π、b2Σ是三个束缚电子态.基态X4Σ的平衡键长为0.2259nm,谐振频率为431cm-1,离解能为1.92eV,目前计算值与实验结果和其它理论值一致.a2Π和b2Σ激发态的核间距、谐振频率分别为0.2447、0.2369nm和329、335cm-1,Te分别为1.58和1.75eV,De则为0.71和0.42eV.A4Π态为排斥态,其相对基态的垂直激发能为2.48eV.通过求解核运动的薛定谔方程找到了转动量子数J=0时NaC分子三个低电子态(X4Σ,a2Π,b2Σ)的全部振动能级和转动惯量.

Potential energy curves （PECs） for the ground electronic state （X4Σ） and the three lowest excited electronic states （a2Π,b2Σ,A4Π） of NaC molecule were calculated using the multi-configuration reference single and double excited configuration interaction method,including Davidson＇s corrections for quadruple excitations （MRCI＋Q）.The equilibrium bond length Re and the vertical excited energy Te were determined directly and the PECs were fitted to an analytical Murrell-Sorbie （MS） potential function to determine the spectroscopic parameters,which were the rotation coupling constant ωe,dissociation energy De,the anharmonic constant ωe χe,the equilibrium rotation constant Be and Drot,and the vibration-rotation coupling constant αe.These values were also compared and were in agreement with other theoretical and experimental results currently available.It is evident that the X4Σ,a2Π,and b2Σ states are bound.We found that in the ground state X4Σ,Re was 0.2259 nm,ωe was 431 cm^-1,and De was 1.92 eV,while in the excited states a2Π and b2Σ,Re and ωe were 0.2447,0.2369 nm and 329,335 cm^-1,respectively.Te was found to be 1.58 and 1.75 eV and De was 0.71 and 0.42 eV.A4Π is a repulsive excited state when Te is 2.48 eV relative to the ground state.By solving the radial Schrdinger equation of nuclear motion the vibration levels and inertial rotation constant at rotational quantum number J=0 are reported for the X4Σ,a2Π,and b2Σ states.