Preparation of CHF (X̃¹A′) by infrared multiphoton dissociation and reactions with alkenes

Abstract

A study of the vibrational, rotational and translational energies of the CHF (z 'A') radical prepared by infrared multiphoton dissociation, IRMPD, is presented. The vibrational and rotational temperatures measured near the CO, laser pulse peak depend on the delay, nature and pressure of the buffer gas. For pure precursor (20 mTorr) and at delays of 0.4 and 3 ps the measured rotational temperatures were 900 and 600 K, respectively. Vibrational temperatures at 3 ps delay for samples of pure precursor (20 mTorr) and of precursor with 1 Torr of Ar were 790 and 630 K.The transient migration method was applied to measure the diffusion coefficient, and hence the collisional diameter, of CHF (R 'A') in Ar. Attempts to measure the average translational energy of the CHF fragment by the same method at low pressures produced extremely low temperatures, and forced a re-examination of the validity of the technique. The average vibrational relaxation rate constant, as determined by the same method and confirmed by direct measurements, gives k , , < cm3 molecule-' s -' , while the rotational relaxation rate constant isk,, > lo-'' cm3 molecule-' s-'.The bimolecular rate constants for removal of CHF (z 'A') with several alkenes are reported to be (/10-l2 cm3 kbutadiene = 22.0 3.0. Some of the reactions are C 0 2 laser fluence dependent, and, in addition, butadiene gives a considerable luminescence. A method is suggested for extrapolation of the apparent kinetic constants to zero fluence to obtain meaningful results. molecule-' S -' ) :kethene = 5.4 f 0.3; kpropene = 13.0 f 1.

Theoretical study on reaction mechanism of the fluoromethylene radical with nitrogen dioxide

“…As a result, such a process can take place at high temperatures. However, for the 1 CHF ϩ NO 2 reaction, the similar product 3 O ϩ HClCNO-trans lies 16.5 kcal/mol above the reactants, indicating that it is less possible for such a process to take place even at high temperatures. Third, for the 1 CHCl ϩ NO 2 reaction, the CON bond cleavage of d 1 (HO(Cl)CNO) to form the product NO ϩ ClCOH plays a role at high temperatures.…”

“…HO(F)CNO), which will easily convert to d 3 followed by a concerted H-shift and CON bond fission to P 2 as in Path2 P 2 , or continuously isomerizes to form d 1 followed by its dissociation to form P 2 as in Path3 P 2. In Path4 P 2 and Path5 P 2 , b can isomerize to c via concerted O-shift followed by a concerted 1,2-H-shift from the O-to N-atom to form e. The isomer e 1 either dissociates directly to give P 2 , or undergo continuous isomerization to form d 3 , followed by its dissociation to form P 2 . As in Path6 P 2 , the direct O-abstraction between 1 CHF and NO 2 can also lead to P 2 .…”

“…First, for 1 CHCl ϩ NO 2 reaction, the product OH ϩ ClCNO cannot be obtained, despite numerous attempts being made to locate the NOO bond cleavage transition state from b (ClC-N(O)OH), while, for the 1 CHF ϩ NO 2 reaction, the product OH ϩ FCNO can be yielded as the second feasible product. Second, for the 1 CHCl ϩ NO 2 reaction, the direct dissociation product 3 O ϩ HClCNO-cis is 0.1 kcal/mol higher than the reactants. As a result, such a process can take place at high temperatures.…”

“…Therefore, Path P 4 may be kinetically the second feasible pathway. The slight difference of Path2 P 2 and Path1 P 5 lies in the last step, that is, the dissociation of d 3 (HO(F)CNO). In terms of the relative energies of TSd 3 P 2 (Ϫ26.9 kcal/mol) and TSd 3 P 5 (Ϫ36.9 kcal/mol), these two pathways may have comparable contribution to the 1 CHF ϩ NO 2 reaction.…”

“…1 Because the large anthropogenic emissions and photolysis of freons as well as further reactions in the stratosphere involving halocarbenes influence the terrestrial atmospheric balance, the studies on halocarbenes have attracted extensive attention both experimentally and theoretically. [2][3][4] Also, the reactions of halocarbenes play an important role in etching of semiconductor material in RF discharges in low pressures. 5 A large number of experimental investigations have been carried out on the simplest fluorocarbene CHF reactions.…”