Neutral mean kinetic energies, ion intensities, and neutral source gas cracking from Ar, N-2, and Cl-2 electron cyclotron resonance (ECR) plasmas, are measured by modulated beam time-of-flight (TOF) analysis. The TOF distributions are characterized by a two component form consisting of an effusive Maxwell-Boltzmann distribution and a fast Gaussian component, that accounts for nonthermal species produced in the source. The mean kinetic energies of neutral species are found to range between 0.04 and 0.45 eV, depending on species and plasma conditions. Mean kinetic energies increase at a nearly constant rate, with decreasing pressure from 8.0 x 10(-2) to 2.5 x 10(-2) Pa with constant applied microwave power. At pressures below 2.5 X 10(-2) Pa, the neutral mean kinetic energies sharply increase. This sharp increase in neutral mean kinetic energy is attributed to an abrupt increase in the ion flux out of the source. The increase in kinetic energy can be separated into two contributions, (i) thermal at higher pressures and (ii) nonthermal at lower pressures. This effect is much stronger for atomic neutrals than for molecular neutrals, where internal degrees of freedom can accept energy in momentum transfer collisions. Cracking of N-2 and Cl-2 is also examined as a function of source pressure at constant microwave power. The N:N-2 flux ratio from the ECR source varies between 0.2 and 1.4. The Cl:Cl-2 flux ratio varies from 10 to 16, indicating a very high degree of dissociation in the plasma. Both flux ratios decrease with increasing source pressure. The total flux of Cl increases with increasing source pressure over the entire range, while the N atom flux peaks at similar to 1.3 X 10(-2) Pa and decreases on either side of this pressure.