Linsen Pei

Kinetics of C2(a3Πu) radical reactions with alkanes by LIF

The reactions of C2(a3Piu) radicals with a series of alkanes have been studied at room temperature and 6.5 torr total pressure using the pulsed laser photolysis/laser-induced fluorescence technique. C2(a3Piu) radicals were generated by photolysis of C2Cl4 with the focused output from the fourth harmonic of a Nd: YAG laser at 266 nm. The relative concentration of C2(a3Piu) radicals was monitored on the (0,0) band of the C2(d3Pig <-- a3Piu) transition at 516.5 nm by laser-induced fluorescence. From the analysis of the relative concentration-time behavior of C2(a3Piu) under pseudofirst-order conditions, the rate constants for the reactions of C2(a3Piu) with alkanes (C1-C8) were determined. The rate constant increases linearly with the increasing of the number of CH2 groups in the alkanes. The experimental results indicate that the reaction of C2(a3Piu) with small alkanes (C1-C8) follows the typical hydrogen abstraction process. Based on the correlation of the experimental results with the bond dissociation energy of the alkanes, the reactions of C2(a3Piu) with small alkanes likely proceed via the mechanism of hydrogen abstraction.

Time-resolved kinetic studies on quenching of NCO (A 2Σ+) by alkanes and substituted methane molecules

NCO radicals were produced by laser photolysis of CHBr3 at 266 nm followed by the reaction of CH with N2O. The radicals were then electronically excited from the ground electronic state to the A 2Σ+ state with a Nd:YAG laser pumped dye laser at 438.6 nm in the Q subband of A 2Σ+(0000)←X 2Πi(0010). The rate constants kq and thermally averaged cross sections σq for collision quenching of NCO (A 2Σ+) by n-CnH2n+2 (n=1,5–8), c-C6H12, CH4−nCln (n=1–4), CH3OH, CH3NO2, and CCl2F2 were measured at room temperature (298 K) by observing the time-resolved fluorescence signals of the excited NCO in a cell at total pressure of about 20 Torr. Formation cross sections of complexes of the electronically excited NCO radicals and quenchers were calculated by means of a collision complex model. It was shown that the quenching rates of NCO (A 2Σ+) by alkane molecules increase with the number of C–H bonds of the molecules, and that the attractive forces play a main role in the collisional quenching processes of NCO (A 2Σ+) by...

Investigation of collisional quenching of CCl2 (Ã 1B1 and ã 3B1) by alkanes

CCl2 free radicals were produced by a pulsed dc discharge of CCl4 (in Ar). Ground electronic state CCl2(X) radical was electronically excited to A 1B1(0,4,0) vibronic state by Nd:YAG laser pumped dye laser at 541.52 nm. The laser induced fluorescence signal is observed to be a monoexponential decay curve corresponding to the decay of the A state under supersonic jet conditions and the lifetime of CCl2(A→X) transition was measured being 0.83±0.03 μs. Experimental quenching data of excited CCl2(A 1B1 and a 3B1) by alkanes were obtained by observing the time-resolved total fluorescence signal of the excited CCl2 radical in a cell, which showed a superposition of two exponential components under the presence of a quencher. The quenching rate constants of A(1B1) and a(3B1) states of CCl2, KA, and Ka, were derived by analyzing the experimental data according to a proposed three-level model to deal with the CCl2(X 1A1,A 1B1,a 3B1) system. KA and Ka increase steadily by increasing the number of C–H bonds conta...

VUV photoionization of (CH3I)n (n = 1-4) molecules

Abstract The photoionization efficiency (PIE) spectra of the ions produced by the VUV synchrotron radiation photoionization of (CH 3 I) n ( n =1–4) molecules in the photon energy range of 8–35 eV have been measured by using time-of-flight (TOF) mass spectrometer with supersonic cooling techniques. The appearance potentials (APs) of all the observed fragment ions have been determined from the PIE curves. Based on these data, the bond energies ( D 0 ), standard formation enthalpies ( Δ f H 0 ° ) and proton affinities (PA 0 ) of the related fragments were obtained. Several autoionization structures of CH 3 I in the PIE spectrum of CH 3 I + were assigned.

Study on resonance-enhanced multiphoton ionization (REMPI) of SO2 in the range 365–405 nm

Abstract The resonance-enhanced multiphoton ionization (REMPI) of SO 2 in the range 365–405 nm has been studied using mass-distinguished excitation spectra. Most of the resonance peaks for both parent ion SO 2 + and fragment ions SO + , S + and O + in the excitation spectra have been assigned to the transition SO 2 ( a 3 B 1 ) ← SO 2 ( X 1 A 1 ) . It has been reasonably assumed that SO 2 (C 1 B 2 ), produced by the subsequent excitation of SO 2 (a 3 B 1 ), plays a key role in generating the fragment ions. It seems that tragment ions come mainly from the photoionization of neutral fragments dissociated from SO 2 (C 1 B 2 ) while the parent ion is formed directly by further photoionization of SO 2 (C 1 B 2 ). That the resonance peaks of the parent ion appear generally narrower than those of fragment ions can also be explained by the known spectral properties of SO 2 (C 1 B 2 ).

The fluorescence excitation spectra of the A 1Au(S1)–X 1Ag(S0) transition of biacetyl: Determination of the band origin

Laser-induced fluorescence spectra of the A 1Au(S1)–X 1Ag(S0) transition of biacetyl are observed under supersonic jet condition. Three weaker bands have been observed at 154, 67, and 58 cm−1 to the red of the previously presumed band origin 000 (at 22 336 cm−1). The observed tunneling splitting 1.05 cm−1 for the G01 band and 1.68 cm−1 for the A01 band are compared to the theoretical result. Based on the tunneling splitting, the true band origin 000 is determined for the first time as the furthest weaker band at 22 182 cm−1. The three weaker bands have been assigned as 000, G01, and A01 transitions, respectively.

Theoretical studies on mechanism for the reaction of the excited nitrogen atom and chloromethane

Abstract The probable reaction mechanism for the reaction of excited nitrogen atom and chloromethane has been studied using the G2MP2 method. Based on the calculated reaction processes, the excited nitrogen atom will insert into the CCl bond firstly to form the intermediate trans -CH 3 NCl, which can subsequently decompose and isomerize to further products. The present result suggests that CH 2 NCl is the most feasible among all possible products. The reaction mechanisms for the N ( 2 D )+ CH 3 X (X=H, F, Cl) system are contrasted in detail.

Resonance multiphoton ionization spectroscopy of the D2Π(v=2)←A2Δ of CH radicals

Abstract The resonance-enhanced multiphoton ionization (REMPI) spectrum of CH was observed in the 240–250 nm region. Rotational analysis of the spectrum indicates that it is due to the D 2 Π( v =2)←A 2 Δ transition. Based on the broad features observed at 247.6 nm while monitoring the C + ion, the previously unreported predissociation Rydberg state at 63600 cm −1 , built upon the excited core of CH + A 1 Π, is discussed.

Kinetics of C2 (a3Πu) radical reactions with NO, N2O, O2, H2 and NH3

AbstractPulsed laser photolysis/laser-induced fluorescence (LP-LIF) is utilized to measure rate constants for C2(a3Πu) reactions with NO, N2O, O2, H2 and NH3. Multiphoton dissociation of C2Cl4 at 266 nm is employed for the generation of C2(a3Πu) radicals. The C2(a3Πu) concentration is monitored by the fluorescence of the (0, 0) band of the (d3Πg↔a3Πu) transition at 516.5 nm. C2(a3Πu) removal rate constants for the reactions are determined as kNO = (5.46 ± 0.10) × 10−11 cm3 molecule−1 s−1,