Excitation Energies and Photoabsorption Oscillator Strengths of the Rydberg Series in CF3Cl. A Linear Response and Quantum Defect Study

Accurate calculation of the ionization energies of the chlorine lone pairs in 1,1,1-trifluoro-2-chloroethane (HCFC-133a)

The vertical ionization energies of the chlorine lone pairs in HCFC-133a have been calculated at the SCF (via Koopmans' theorem and including orbital relaxation) and correlated (ROMP2, OVGF, and ROCCSD(T)) levels. Dunning aug-cc-pVXZ (X = D, T, and Q) basis sets were employed, and the ROMP2 and ROCCSD(T) results were extrapolated to the complete basis set (CBS) limit. Our highest-level results (obtained at the ROCCSD(T)/CBS level) were 11.99 and 12.08 eV for the Cl lone pairs of A″ and A' symmetry, respectively. The values obtained at the computationally much less demanding ROMP2/CBS level were just 0.10 and 0.13 eV higher than the highest-level ones. Using the Cl lone-pair band of the photoelectron spectrum of the HCF(2)Cl and CF(3)Cl molecules as a guide, it is considered very unlikely that these two lone pairs can be discriminated in the photoelectron spectrum of the title molecule. The use of the calculated IPs to estimate the energies of the Rydberg states of HCFC-133a is also discussed.

Matrix isolation infrared spectroscopic and theoretical study of 1,1,1-trifluoro-2-chloroethane (HCFC-133a)

The molecular structure and infrared spectrum of the atmospheric pollutant 1,1,1-trifluoro-2-chloroethane (HCFC-133a; CF3CH2Cl) in the ground electronic state were characterized experimentally and theoretically. Excited state calculations (at the CASSCF, MR-CISD, and MR-CISD+Q levels) have also been performed in the range up to ~9.8 eV. The theoretical calculations show the existence of one (staggered) conformer, which has been identified spectroscopically for the monomeric compound isolated in cryogenic (~10 K) argon and xenon matrices. The observed infrared spectra of the matrix-isolated HCFC-133a were interpreted with the aid of MP2/aug-cc-pVTZ calculations and normal coordinate analysis, which allowed a detailed assignment of the observed spectra to be carried out, including identification of bands due to different isotopologues ((35)Cl and (37)Cl containing molecules). The calculated energies of the several excited states along with the values of oscillator strengths and previous results obtained for CFCs and HCFCs suggest that the previously reported photolyses of the title compound at 147 and 123.6 nm [T. Ichimura, A. W. Kirk, and E. Tschuikow-Roux, J. Phys. Chem. 81, 1153 (1977)] are likely to be initiated in the n-4s and n-4p Rydberg states, respectively.

Full configuration interaction calculation of the low lying valence and Rydberg states of BeH

The all-electron full configuration interaction (FCI) vertical excitation energies for some low lying valence and Rydberg excited states of BeH are presented in this article. A basis set of valence atomic natural orbitals has been augmented with a series of Rydberg orbitals that have been generated as centered onto the Be atom. The resulting basis set can be described as 4s2p1d/2s1p (Be/H) + 4s4p3d. It allows to calculate Rydberg states up to n= {3,4,5} of the s, p, and d series of Rydberg states. The FCI vertical ionization potential for the same basis set and geometry amounts to 8.298 eV. Other properties such as FCI electric dipole and quadrupole moments and FCI transition dipole and quadrupole moments have also been calculated. The results provide a set of benchmark values for energies, wave functions, properties, and transition properties for the five electron BeH molecule. Most of the states have large multiconfigurational character in spite of their essentially single excited nature and a number of them present an important Rydberg-valence mixing that is achieved through the mixed nature of the particle MO of the single excitations.