используя sapply
x <- seq(1.1, 1.7, by = .1)
sapply(x, optimize, f = objective.function, interval = c(0,1))
или используя purrr
library(purrr)
map(x, ~optimize(f = objective.function, interval = c(0,1), R0 = .x))
или
map_dfr(x, ~optimize(f = objective.function, interval = c(0,1), R0 = .x))