Measurements of $${\mathrm {B}} ^{*}_{{\mathrm {s}}2}(5840)^0 $$ and $${\mathrm {B}} _{{\mathrm {s}}1}(5830)^0 $$ mesons are performed using a data sample of proton-proton collisions corresponding to an integrated luminosity of , collected with the CMS detector at the LHC at a centre-of-mass energy of $$8\,\text {TeV} $$ . The analysis studies P-wave $${\mathrm {B}} ^0_{\mathrm {s}} $$ meson decays into $${\mathrm {B}} ^{(*)+} \mathrm {K} ^- $$ and $${\mathrm {B}} ^{(*)0} \mathrm {K} ^0_{\mathrm {S}} $$ , where the $${\mathrm {B}} ^+ $$ and $${\mathrm {B}} ^0 $$ mesons are identified using the decays $${\mathrm {B}} ^+ \rightarrow {\mathrm {J}}/\psi \mathrm {K} ^+ $$ and $${\mathrm {B}} ^0 \rightarrow {\mathrm {J}}/\psi \mathrm {K} ^{*}(892)^0 $$ . The masses of the P-wave $${\mathrm {B}} ^0_{\mathrm {s}} $$ meson states are measured and the natural width of the $${\mathrm {B}} ^{*}_{{\mathrm {s}}2}(5840)^0 $$ state is determined. The first measurement of the mass difference between the charged and neutral $${\mathrm {B}} ^{*} $$ mesons is also presented. The $${\mathrm {B}} ^{*}_{{\mathrm {s}}2}(5840)^0 $$ decay to $${\mathrm {B}} ^0 \mathrm {K} ^0_{\mathrm {S}} $$ is observed, together with a measurement of its branching fraction relative to the $${\mathrm {B}} ^{*}_{{\mathrm {s}}2}(5840)^0 \rightarrow {\mathrm {B}} ^+ \mathrm {K} ^- $$ decay.