Multireference configuration interaction studies of HCBr

Abstract

Multireference configuration interaction (MRCI) potential curves were obtained for six 1 A , 1 A , 3 A , and 3 A states of bromomethylene, HCBr, as functions of R CBr for bond angles of 102.9 • and 130 • , and as functions of the bond angle for R CBr = 1.8682 Å. A (6.61) (with estimated upper limits to the adiabatic transition energies in eV in parentheses), as well as several 5s and 6s Rydberg states, were found to be stable or metastable. Estimated spectroscopic constants for bound and metastable states, as well as vertical excitation energies for repulsive or quasi repulsive states are listed. The CH+Br dissociation energy of the ground state is about 3.5 eV, and 3.3 eV for a 3 A , whereas it is about 3.6 eV for CBr-H dissociation. It follows that photodissociation of ground-state HCBr by sunlight (up to 4.4 eV) can lead to both Br and H radicals. Photodissociation via several low-lying states is also possible.Résumé : Nous avons obtenu les courbes de potentiel pour les états 1 A , 1 A , 3 A et 3 A du bromoéthylène, HCBr, en fonction de R CBr pour les angles de lien de 102.9 et 130 degrés et comme fonction de l'angle de lien pour R CBr = 1, 8682 Å. En plus des états bien connus X 1 A , a 3 A et A 1 A , nous avons trouvé comme étant stables ou métastables les états 2 1 A (6,61) (les quantités entre parenthèse donnant en eV la limite supérieure des énergies de transition adiabatique), ainsi que plusieurs états de Rydberg 5s et 6s. Nous présentons la liste d'un estimé des constantes spectroscopiques pour les états liés et métastables, ainsi que des énergies d'excitation verticale pour les états répulsifs ou quasi-répulsifs. L'énergie de dissociation pour le fondamental de CH+Br est environ 3,5 et 3,3 eV pour l'état a 3 A , alors qu'il est 3,6 eV pour la dissociation de CBr-H. Il s'ensuit que la photodissociation du fondamental de HCBr par la lumière solaire (jusqu'à 4,4 eV) peut mener aux radicaux Br et H. La photodissociation via plusieurs états de basse énergie est également possible.[Traduit par la Rédaction]

Multireference Configuration Interaction Study of Bromocarbenes

“…Geometries of all compounds obtained in the current work are in generally good agreement with the myriad of previous computational studies of bromocarbenes carried out in recent years using a variety of theoretical methods. − ,− It is observed that C−Br bond distances are generally shorter by 0.01−0.04 Å and bond angles slightly larger by less than 1° (and closer to available experimental results) for calculations employing triple-ζ plus polarization quality basis sets compared to results obtained using double-ζ plus polarization basis sets.…”

“…Equilibrium geometries and a detailed analysis of the potential surfaces of the ground X̃( 1 A′) and excited Ã( 1 A′′) singlet states as well the lowest ã( 3 A′′) triplet state of CHBr were presented. In recent work by Burrill and Grein, a TZP basis set with polarization and diffuse functions was employed in order to carry out MRCI calculations on the lowest six singlet and triplet electronic states of CHBr. For CFBr, the MRCI method with an active space of two electrons in two orbitals, MRCI(2,2), and a TZP quality basis set was employed to study only the first excited Ã( 1 A′′) singlet state .…”

“…Higher level multireference configuration interaction (MRCI) calculations have been previously completed only for CHBr, 14,15 CFBr, 12 and CClBr. 16 In work by Yu et al, 14 MRCI calculations were carried out on CHBr with a cc-pVTZ basis set using state-averaged full-valence active space CASSCF reference functions.…”

An ab Initio Investigation of Fluorobromo Carbene

“…Due to the numerous interactions between the electronic states, such as Renner–Teller effect, spin–orbit coupling, avoided crossing, or nonadiabatic interaction leading to predissociation, the spectroscopy and photodissociation dynamics of halocarbenes are rather complicated, which stimulate scientists to continuously perform experimental and theoretical studies on these important reactive intermediates. During past several decades, with the advances of high-resolution laser-based spectroscopic techniques along with theoretical methods, a variety of halocarbenes, including monohalogenated carbenes CHF − /CHCl − /CHBr − /CHI, dihalogenated carbenes CCl 2 , − CBr 2 , CFCl, CFBr, − and CFI, and so on, have been widely investigated by using, for example, rotational-resolved laser absorption, laser-induced fluorescence (LIF), optical–optical-double-resonance (OODR), and stimulated emission pumping (SEP) techniques, as well as ab initio calculations. − The structure, spectroscopy, and interactions of the ground state and the lowest singlet/triplet excited states of the halocarbenes have been studied comprehensively. Although sparse studies concerning higher excited states have emerged, for example, photodissociation dynamics of CHF and CDF at the B state, − CCl 2 at 248 nm , and 193 nm, and CHCl, CFCl, and CFBr at 193 nm …”

A combined ab initio and Franck–Condon simulation study of the photodetachment spectra of the HCBr− anion

“…At present, most researches were focus on the neutral molecules HCBr [15][16][17][18][19][20][21], and its corresponding negative ion HCBr − were relatively sparse [22][23][24][25]. In 1992, Gilles reported the photoelectron spectra, geometrical structures and corrected adiabatic electron affinity for the singlet state of HCBr [23].…”