The equation maintains the same form as previous theoretical studies on related property , with quite perfect fitting quality of R 2 > 0.999. The numerical result obtained by substituting n = 15 into the fitting equation is 341.0 nm, which is also in good agreement with the DFT result calculated directly (338.9 nm). Therefore the equation fitted herein should be robust and useful for predicting 1 1 Σ u + ← X 1 Σ g + absorption wavelengths of carbon chains of arbitrarily length. By extrapolation, the asymptotic value of 389.5 nm is found from Eq. (3) for the infinite length carbyne.