The molecular structure of chloronitromethane was studied in the gas phase at a nozzle-tip temperature of 373 K. The experimental data were interpreted using a dynamic model where the molecules are undergoing torsional motion governed by a potential function: V = V-2/2x(1 - cos 2 tau) + V-4/2x(1 - cos 4 tau) with V-2 = 0.81(30) and V-4 = 0.12(40) kcal/mol (tau is the dihedral angle between the C-Cl and N-O bond). The conformer with a zero degree dihedral angle is the most stable conformer. Comparison with results from HF/MP2/B3LYP 6-311G(d,p) calculations were made. The important geometrical parameter values ( for the eclipsed form) obtained from least-squares refinements are the following: r(C-H) = 1.061(18) angstrom, r(C-N) = 1.509 (5)angstrom, r( N-O) = 1.223(1)angstrom, r(C-Cl) = 1.742(2)angstrom, angle ClCN = 115.2(7)degrees, angle O4NC = 118.9(10)degrees, angle O5NC = 114.9(16)degrees, and angle ClCH 115(4)degrees.