Gas-phase kinetics are reported for the reactions of Ti(a3F) with 0 2 , N20, NO, CO,, S02, and NO2 from 300 to 600 K. Titanium atoms were produced by the photolysis of T i c 4 at 248 nm and were detected by laserinduced fluorescence. Arrhenius expressions obtained for these reactions at a buffer gas pressure of 20 Torr are k(O2) = (1.69 f 0.41) X exp(-(14.3 f 0.9 kJ/mol)/RTcm3 s-l, k(N0) = 3.28 f 0.69) X exp(-(3.62 f 0.71 kJ/mol)/RT) cm3 s-l, k(CO2) = (7.0 f 1.6) X exp(-(2.66 f 0.64 kJ/mol)/RT) cm3 s-l. The rate constant of Ti with NO2 was found to be temperature independent from 300 to 500 K with a value of (9 f 4) X cm3 s-l. Quoted uncertainities are f2u. With the exception of Ti + 0 2 , all reactions were investigated as a function of pressure. Only the reactions of Ti with NO and C02 were found to depend on the argon buffer gas pressure. Termolecular rate constants at 300 Kweredeterminedtobe(5.8 f 2.6) X 10-31cm6s-1 and(3.5 f 1.0) X 10-32cm6s-1 forNOandCO2,respectively. exp(-(11.6 f 0.8 kJ/mol)/RT) cm3 s-l, k(N2O) = (1.74 f 0.44) X exp(-(14.9 f 0.8 kJ/mol)/RT) cm3 s-l, and k(SO2) = (1.70 f 0.33) X

The gas-phase reactivities of W(a 5D,, a 7S3) with O2 in the temperature range 298-573 K are reported. Tungsten atoms were produced by the photodissociation of W(CO), and detected by laser-induced fluorescence. The disappearance rate constant of the s1d5 a ' S , state is of the order of the gas kinetic rate constant. The removal rate constants for the s2d4 a 5D, states are J dependent. The a 5D, states are not as reactive as the s1d5 a 'S3 state and are found to be temperature dependent. The disappearance rates of all states in the presence of O2 are found to be pressure independent with buffer gas. Physical quenching rate constants for the excited states in the presence of Ar, He, N, and sF6 are also reported. Results are discussed in terms of the different electron configurations of the states.

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The gas phase depletion kinetics of Nb(a6D J ,a4F J ) in the presence of O2, SO2, CO2, N2O, and NO are reported. Niobium atoms were produced by the 248 nm photodissociation of Nb(C5H5)(CO)4 and detected by laser-induced fluorescence. The ground term of Nb(4d45s a6D J ) reacts at or above the collision rate with all of the aforementioned oxidants. The first excited term, Nb(4d35s a4F J ), is not as reactive with these oxidants. Results are interpreted in terms of long-range attractions and valence interactions. Additionally, we report reaction rate constants for ground state Nb interacting with N2, CH4, and SF6. Nb(a6D J ) is unreactive toward CH4. Nb(a6D J ) + N2 is pressure dependent at 297 K with k 0 = (2.6 ± 0.3) × 10-32 cm6 s-1 and k ∞ = (4.1 ± 0.5) × 10-13 cm s-1. Nb(a6D J ) + SF6 is temperature dependent with the rate constants given by k(T) = (1.2 ± 0.3) × 10-10 exp[−(4.8 ± 0.2) kcal mol-1/RT] cm3 s-1. Depletion of the aF J term by N2, SF6, and CH4 is J-dependent.

The gas-phase kinetics are reported for the reactions V(a4F3/,) + OX, where X = 0, N, and CO, in the temperature range 297-643 K. V atoms were produced by the multiphoton dissociation of VC14(g) at 193 nm and were detected by laser-induced fluorescence. Arrhenius rate expressions obtained for these reactions are k(Oz) = (1.20 f 0.26) X exp[-(2.16 f 0.19 kcal/mol)/RT] cm3 s-I, k(N0) = (2.20 f 0.26) X 10-l' exp[-(0.40 f 0.19 kcal/mol)/RT] cm3 s-I, and k(COz) = (4.38 f 0.62) X lo-" exp[-(2.90 f 0.14 kcal/mol)/RT]cm's-'. Also, room temperature rate constants were measured for the disappearance of the excited state V(a6D3/2) due to collisions with OX, Ar, and N2; the V* disappearance rates induced by collisions with the oxidants are found to be considerably faster than those of the ground-state atom, with rate constants (in units of cm3 s-I) k(Oz) = (1.34 f 0.21) X k(C02) = (2.17 f 0.35) X 10-l'. k(Ar) = (2.06 f 0.32) X Quoted uncertainities are f2a. The rates of collisional quenching are compared to the reaction rates of ground-state vanadium, and quenching mechanisms are discussed. k(N0) = (1.00 f 0.16) X and k(Nz) = (5.62 f 0.83) X