Rotational structure in the Ã1A″–X̃1A′ spectrum of formyl chloride

Abstract

High-resolution cavity ring-down spectroscopy has been used to record three vibronic bands of the transition of room-temperature formyl chloride (HClCO). These three bands A 3 1AAÈX 3 1A@ (p* ^nO ) (6 0 1 , 5 0 1 6 0 1 and are all vibronically induced through the activity of the out-of-plane inversion vibration and 2 0 1 5 0 1 6 0 1) l 6 , are found to obey type-a selection rules. Rotational constants have been derived from the analysis of these bands and used to give information on the geometrical structure of the excited state. The properties of the A 3 state are found to be intermediate between those of the corresponding states of formaldehyde and formyl Ñuoride.

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

“…They show that for systems under investigation, such combination of method and basis cannot be considered as sufficiently accurate, because the differences between experimental and theoretical bond lengths and barrier heights are significant for all molecules where the experiment is available. EOM-CCSD/ccpVTZ method systematically underestimates, comparing where available with experiment, practically all the bond lengths (Table V) (1.310 Å) appeared to be in good agreement with experimental estimation [3], but this experimental value cannot be considered as reliable and is in disagreement with our refinement of experimental structure (see section 3.3). As for out-of-plane CAO or COH (see footnotes to Table V), one can conclude that calculations on double-basis level are in excellent agreement with experiment while within triple-agree worse.…”

“…(6-5) AS was confirmed to be stable by calculations of large areas of excited state PES (will be published in next communica- The overall accuracy of the CASSCF(6-5) method seems to be poor mainly due to the poor evaluation of CAO bond lengths (in all states) and barriers to inversion (in T 1 and S 1 ). CASSCF tends to significantly overestimate r(CAO): for example, for H 2 CO (S 1 ) difference between experimental and calculated results is 0.057 Å; for HFCO (S 1 ), 0.045 Å; and for HClCO (S 1 ), 0.072 Å when compared with experiment [3] and 0.035 Å when compared with refined structure (see section 3.3 and Table VIII). Moreover, the difference between experimentally determined and calculated V i is about 10 -70% (see Fig.…”

“…Note that the excitation changes occupancy numbers within the valence shell; configurations for halogen derivatives are similar to those of formaldehyde. The symmetrical systems X 2 CO in the ground state S 0 are classified as 1 A 1 type (C 2v point group of the equilibrium nuclear configuration), the excited states are classified as 1,3 AЉ (S 1 , T 1 ) (C s -symmetry) and 1,3 A 2 (S 1 , T 1 ) for plane transition states (C 2v -symmetry). For asymmetrically substituted molecules XYCO, the ground state is classified as 1 AЈ (C ssymmetry), plane transition states (C s -symmetry) as 1,3 AЉ (S 1 , T 1 ), but there is not any point symmetry for S 1 and T 1 minima.…”

“…It was proved experimentally for H 2 CO [1], HFCO [2], HClCO [3], and wide variety of other aliphatic carbonyls (for review, see Ref. [4]) that electronic excitation from the ground (S 0 ) to the lowest excited singlet (S 1 ) and triplet (T 1 ) states results in lengthening of CAO distance and pyramidalization of the carbonyl fragment planar in S 0 state.…”

“…[10] and [11]). Experimental geometries of H 2 CO, HFCO, and HClCO molecules in S 1 electronic state were evaluated on the basis of analysis of rotational structure [1][2][3] of vibronic bands. For evaluation of some parameters additionally, the calculations of intensities of vibronic bands [2,3] were carried out, and analogies in structure of related molecules HFCO and HClCO were taken into account [3].…”