Kinetic isotope effect (KIE) and reaction,rate coefficients, k(1)-k(4), for the gas-phase reaction of Cl atoms With (CH3D)-C-12 (k(1)), (CH2D2)-C-12 (k(2)), and (CD4)-C-12 (k(4)) over the temperature range 223-343 K in 630 Torr of synthetic air are reported. Rate coefficients were measured using a relative rate technique with (CH4)-C-12 as the primary reference compound. Fourier transform infrared spectroscopy Was used to monitor the methane isotopologue loss. The obtained KIE values: were (CH3D)-C-12: KIE1(T) = (1.227 +/- 0.004) exp((43 +/- 5)/T); (CH2D2)-C-12: KIE2(T) = (1.14 +/- 0.20) exp((191 +/- 60)/T); (CH3D)-C-12: KIE3(T) = (1.73 +/- 0.34) exp((229 +/- 60)/T); and (CD4)-C-12: KIE4(T) = (1.01 +/- 0.3) exp((724 +/- 19)/T), where KIEx(T) = k(Cl+)(CH4)(12) (T)/k(x)(T). The quoted uncertainties are at the 2 sigma (95% confidence) : level and represent the precision of our data. The following Arrhenius expressions and 295 K rate Coefficient values (in unit of cm(3) molecule(-1) s(-1)) were derived from the above KIE using a rate coefficient of 7.3 x 10(-12) exp(-1280/T) cm(3) molecule(-1) s(-1) for the reaction of Cl with (CH4)-C-12: k(1)(T) = (5.95 +/- 0.70) x 10(-12) exp(-(1323 +/- 50)/T), k(1)(295 K) = (6.7 +/- 0.8) x exp(-(1509 +/- 60)/T); k(3)(295 K) = (2.53 +/- 0.6) x 10(-14); and k(4)(T) = (7.13 +/- 2.3) x 10(-12) exp(-(2000 +/- 120)/T), k(4)(295 K) = (0.81 +/- 0.26) x 10(-14). The reported uncertainties in the pre-exponential factors are 2 sigma and include estimated systematic errors in our measurements and the uncertainty in the reference reaction rate coefficient. The results from this study are compared with previously reported room-temperature-rate coefficients for each of the deuterated methanes as well as the available temperature dependent data for the Cl atom reactions with CH3D and CD4. A two-dimensional atmospheric chemistry model was used to examine the implications of the present results to the atmospheric, lifetime and vertical variation in the loss of the deuterated methane isotopologues. The relative contributions of the reactions of OH, Cl, and O(1(D)) to the loss of the isotopologues in the stratosphere were also examined. The results, of the calculations are described and discussed.