Rate constants for the collisional deactivation of spin-orbitally excited Cl* (equivalent to Cl(P-2(1/2))) atoms by some selected gases have been determined using time-resolved laser magnetic resonance (LMR) techniques. Cl* atoms were produced by photodissociation of ICl at 248 nm, and the relative quantum yield of Cl* atoms is determined to be 0.47 +/- 0.06. The rate constants for the relaxation of Cl* (x10(-11) cm(3)/molecule.s, +/- 2 sigma) by H-2(5.5 +/- 1.6), HF(1.4 +/- 0.4), DF(0.7 +/- 0.2), DCl(0.7 +/- 0.2), HBr(1.2 +/- 0.36), DBr(1.4 +/- 0.4), NO(0.66 +/- 0.2), SO2 (1.9 +/- 0.5), N2O (0.63 +/- 0.2), NF3 (22 +/- 6), CH4 (1.9 +/- 0.6), CD4 (13 +/-4), CF4 (2.4 +/- 0.7), SiF4 (14 +/- 4), and SF6 (18 +/- 5) at 298 K are reported. The rate constants of the reactions of ground state Cl(P-2(3/2)) atoms with HBr and DBr were found to be, in units of x10(-11) cm(3)/molecule.s, 0.75 +/- 0.15 and 0.50 +/- 0.10, respectively. The study of the deactivation process I(P-2(1/2))+ICl --> Cl-*+I-2 (a), Cl+I-2 (b), I+ICl (c) yielded the ratios k(a)/(k(a)+k(b))=0.63 +/- 0.17, k(a)/(k(a)+k(b)+k(c))greater than or equal to 0.70. (C) 2000 American Institute of Physics. [S0021-9606(00)01406-9].