ICR studies of some hydrogen atom abstraction reactions: X+ + H2 → XH+ + H

Abstract

Ion cyclotron resonance methods are used to identify and to measure the rate constants for the abstraction of a hydrogen atom from H2 by CH+, CH2+, CH4+, N+, NH+, NH2+, NH3+, O+, OH+, H2O+, CO+, N2+, C2+, and C2H+ ions. Although in most cases hydrogen atom abstraction is the only available exothermic pathway for these reactions at thermal energies, the rate constants measured show that except for O+, CO+, and N2+, a large fraction of collisions between these ions and H2 are not reactive. The rate constants measured range from a low of (3±1) × 10−13 cm3/sec for the NH3+−H2 reaction to (1.73±0.04) × 10−9 cm3/sec for the N2+−H2 reaction. These values compare to the Langevin value of about 1.5 × 10−9 cm3/sec for collisions between these ions and H2. An examination was also made for possible thermoneutral hydrogen atom exchange reactions for those ions which do not react with H2 (CH5+, CH3+, NH4+, H3O+, H2S+, H3S+). The only exchange reaction observed was for collisions between CD3+ ions and H2, for which a rate constant of (5.1±0.5) × 10−10 cm3/sec was measured.

Experimental and Theoretical Kinetics for the H2O+ + H2/D2 → H3O+/H2DO+ + H/D Reactions: Observation of the Rotational Effect in the Temperature Dependence

“…The current measurement for the reaction with H 2 agrees well with previous measurements by 6.1, 10 The temperature dependences of both reaction rate coefficients are shown in Fig. 2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 9 which is common for ion-molecule reactions), and that the experimental errors represent normal distributions, it is highly likely (>95%) that the data between 110 K and 350 K follow a positive temperature dependence and quite likely (>80%) that the data from 350 K to 600 K follow a negative temperature dependence.…”

“…Rakshit and Warneck13 and Kim et al,10 but only just agrees with the previous SIFT measurement byJones et al 14 within the combined uncertainties. The current rate coefficient for…”

“…So far, however, the rate coefficients have mostly been measured near room temperature and the experimental data contain large uncertainties. [7][8][9][10][11][12][13][14] In addition, the title reactions have been used to investigate mode specificity in reaction dynamics thanks to advances in laser technology that allow selective population of single quantum states. [15][16] The effects of translational, rotational, and vibrational excitations on reactivity have been systematically investigated.…”

Low temperature rates for key steps of interstellar gas-phase water formation

“…One potentially significant difference between our data and almost all previous studies [except for the room temperature ion cyclotron resonance measurements of Kim et al . ( 19 )] is the pressure regime. While the number densities in all experiments are orders of magnitude higher than in interstellar space, the H 2 density in our studies was below 10 11 cm −3 , and the helium buffer gas density was on the order of 10 13 cm −3 .…”

“…The published values show a significant scatter, and we refrain from addressing all of the individual measurements here (we will discuss the overall trends in Results and Discussion). In summary, the rate coefficients published for reaction (1) range from k 1 = 8.6 × 10 −10 cm 3 s −1 ( 16 ) to k 1 = 1.5 × 10 −9 cm 3 s −1 ( 17 ), while rate coefficients for reaction (2) range from k 2 = 4.0 × 10 −10 cm 3 s −1 ( 18 ) to k 2 = 1.4 × 10 −9 cm 3 s −1 ( 17 ), with additional values between these two extremes ( 14 , 19 , 20 ). …”