Conformational changes accompanying electronic excitation of trifluoronitrosomethane

Abstract

The 690 nm absorption spectrum of CF3NO has been studied in the gas phase at various temperatures and in the condensed phase at 77 K, and assigned to an (nπ*) transition. Analysis of the vibrational structure shows that, while only the eclipsed conformer is stable in the ground state, there are two stable isomers of comparable energy in the excited electronic state. One has an eclipsed conformation, but with the CF3 group tilted away from the oxygen atom. The other has a staggered conformation. In both of the excited state isomers the barrier to internal rotation is higher than in the ground state.

Spectra and Photochemistry of Trifluoronitrosomethane Adsorbed on Alkali Halide Films

“…The S 1 fluorescent rate constant for the compound is estimated to be 3.3 × 10 4 s -1 based on the gas-phase oscillator strength , 6 while the gas-phase photochemical (fragmentation) rate constants for CF 3 NO have been determined to be 2.3 × 10 8 s -1 at 633 nm and 5.4 × 10 7 s -1 at 670 nm: 18 fluorescence will constitute a slight correction to the relaxation rate in this scheme. Assuming steady-state concentrations of the radical and excited-state species in eq 9, the concentration expressions become and The quantum efficiency expression in eq 9 becomes which may be solved for k r to give…”

“…Our excitations occur at 15 794 and 14 921 cm -1 , corresponding to the gas-phase transitions [7 0 2 ,4 0 1 ,1 0 1 ] and [7 0 1 ,4 0 1 ], respectively. 6 The rate constant expression used by Roellig and co-workers 19 should be applicable in this case:…”

“…[10][11][12][13][14] The blue color of the gas is attributed to a weakly allowed transition to the A 1 A′′-(nπ*) state at 690 nm. 6 Facile decomposition of the compound occurs from this state in the gas phase, 5 presumably through intersystem crossing to the corresponding triplet state (1130 nm), 7 although there has been indication that internal conversion into the ground state may also play a role. 15 The energy distribution into the CF 3 and NO photoproducts has been well characterized.…”

One-dimensional models of internal rotation in CX3NO molecules (X=H, D, F)

“…These molecules are sufficiently small for high-level ab initio calculations and they are characterized by a simple form of the internal rotation potential. In addition, the structures of the molecules under consideration were experimentally studied by microwave [1,2], vibrational [3,4], and vibronic [5][6][7][8][9][10] spectroscopy.…”

“…We used the results of the studies [1][2][3][4][5][6][7][8][9][10] for comparison with the results of ab initio calculations. Before proceeding to numerical experiments (Section 3), let us describe the concepts forming the background for the use of one-dimensional potential curves for internal rotation.…”