¹⁵N spin relaxation data have provided a wealth of information on protein dynamics in solution. Standard R₁, R_1ρ, and NOE experiments aimed at ¹⁵N[¹H] amide moieties are complemented in this work by HA(CACO)N-type experiments allowing the measurement of nitrogen R₁ and R_1ρ rates at deuterated ¹⁵N[²D] sites. Difference rates obtained using this approach, R₁(¹⁵N[¹H]) - R₁( ¹⁵N[²D]) and R₂(¹⁵N[¹H]) - R₂(¹⁵N[²D]), depend exclusively on dipolar interactions and are insensitive to ¹⁵N CSA and R_ex relaxation mechanisms. The methodology has been tested on a sample of peptostreptococcal protein L (63 residues) prepared in 50% H₂O-50% D₂O solvent. The results from the new and conventional experiments are found to be consistent, with respect to both local backbone dynamics and overall protein tumbling. Combining several data sets permits evaluation of the spectral density J(ω_D + ω_N) for each amide site. This spectral density samples a uniquely low frequency (26 MHz at a 500 MHz field) and, therefore, is expected to be highly useful for characterizing nanosecond time scale local motions. The spectral density mapping demonstrates that, in the case of protein L, J(ω_D + ω_N) values are compatible with the Lipari-Szabo interpretation of backbone dynamics based on the conventional ¹⁵N relaxation data.