Theoretical study of structures of the X2CO and XYCO molecules (X and Y = H, F, or Cl) in the ground and lowest excited triplet electronic states

Abstract

Systematic calculations of the structures of the H 2 CO, F 2 CO, Cl 2 CO, HClCO, HFCO, and FClCO molecules in the S 0 and T 1 states were performed using the B3LYP and MP2 methods with different AO basis sets and also at the CCSD(T)/cc pV(T+d)Z level of theory. The saturation of the correlation consistent sequence of basis sets cc pV(N+d)Z (N = D, T, Q, and 5) and aug cc pV(N+d)Z (N = D, T, and Q) was studied. Recommendations for choosing the calculation method are given. The relativistic corrections were estimated. The influence of the number and type of halogen atoms on the geometric parameters of the molecules in the S 0 and T 1 states and the heights of inversion barriers in the T 1 state was investigated.Key words: quantum chemical calculations, systematic basis sets, structures of molecules in excited electronic states, inversion motion, formaldehyde, halogen substituted formalde hydes.Experimental studies of vibronic spectra of carbonyl compounds demonstrated that the carbonyl fragment in particular compounds becomes nonplanar upon excita tion from the ground (S 0 ) to the lowest triplet (T 1 ) and singlet (S 1 ) electronic states due to which a large ampli tude internal motion, viz., the inversion of the nonplanar carbonyl fragment, can occur. 1 The molecules of formaldehyde (H 2 CO) and its halo gen substituted derivatives are the simplest representa tives of carbonyl compounds and serve as convenient mod els for studying the structural features of this class of mol ecules. Many of these compounds have found use in in dustry as chemicals for organic synthesis (for example, phosgene Cl 2 CO is used as the starting material in the production of dyes, polycarbonates, urea and its deriva tives, pesticides, drugs, solvents, etc.). Some of them are generated upon photolysis and oxidation of fluoro and chloro derivatives of hydrocarbons, including freons, in the troposphere and stratosphere; it is supposed that these compounds catalyze ozone decomposition. 2-5 Hence, the physical and chemical properties of these compounds are of considerable interest.Earlier, the molecules of halogen substituted formal dehydes have been studied primarily in the ground elec tronic state by vibrational spectroscopy and gas electron diffraction. 6-10 The structure of the H 2 CO molecule in the S 0 state has been investigated in depth by micro wave and rovibrational spectroscopy. 11 Analysis of the rovibronic spectra provided information 11 on the struc tures of these molecules in the S 1 and (only for formalde hyde) T 1 states. We performed theoretical study of the structures and vibrational dynamics of formaldehyde and its halogen substituted derivatives in the S 0 and T 1 states. Our investigation included two steps. In the first step, we estimated the reliability of different methods for solving the electronic Schroedinger equation. In the second step, the chosen methods were used for studying the potential energy surface (PES) in the region, where vibrational wavefunctions are localized, and solved the nuclear Schroedinger equ...

Molecular parameters of tetraatomic carbonyls X2CO and XYCO (X, Y = H, F, Cl) in the ground and lowest excited electronic states, part 1: A test ofab initiomethods

“…According to Ref. 34 (for S 0 and T 1 ) and our preliminary analysis (for S 1 ), the cc-pVTZ and cc-pVQZ basis sets are close to saturation for the systems and states studied here.…”

“…[34] devoted to study of MP2 performance and basis set saturation for formaldehyde and its halogenated derivatives in S 0 and T 1 electronic states. The simplest correlation effects analysis at the MP2/cc-pVTZ level (see, e.g., Table II) gives much better agreement for all parameters, and the result does not depend on the basis set (cc-pVTZ or 6-311G(d,p)).…”

“…The results of CCSD calculations are mentioned sometimes for comparison and are presented in the text only. Earlier for ground state of H 2 CO [36], HClCO [6], and FClCO [9] calculations of molecular geometry on the same or even better level were published; the systematic investigation of all six molecules in S 0 and T 1 states was reported [34] at CCSD(T)/cc-pVTZ level.…”

“…Earlier [34] relativistic corrections on MP2/cc-pVQZ-DK2 level for X 2 CO and XYCO molecules in S 0 and T 1 states were considered. For geometrical parameters, these corrections are about 0.001 Å and 0.1°or less.…”

“…In accordance with basis set saturation analysis [34], we carried out EOM-CCSD/cc-pVTZ calculations for all systems under investigation in the S 1 state. Some geometrical parameters, barriers, and transition energies are presented in Table V.…”