We have reinvestigated the A ^ { 1 } \Pi ( v = 0 ) level of ^ { 13 } C ^ { 18 } O using new high-resolution spectra obtained via multi-photon laser excitation as well as with synchrotron-based Fourier-transform absorption spectroscopy of the A ^ { 1 } \Pi - \textrm { X } ^ { 1 } \Sigma ^ { + } ( 0 , 0 ) , e ^ { 3 } \Sigma ^ { - } - \textrm { X } ^ { 1 } \Sigma ^ { + } ( 1 , 0 ) , d ^ { 3 } \Delta - \textrm { X } ^ { 1 } \Sigma ^ { + } ( 4 , 0 ) , a ^ { \prime 3 } \Sigma ^ { + } - \textrm { X } ^ { 1 } \Sigma ^ { + } ( 9 , 0 ) , and a ^ { 3 } \Pi - \textrm { X } ^ { 1 } \Sigma ^ { + } ( 11 , 0 ) bands .
In addition , Fourier-transform emission spectroscopy in the visible range is performed on the { B } ^ { 1 } \Sigma ^ { + } - { A } ^ { 1 } \Pi ( 0 , 0 ) band .
Spectra of the B ^ { 1 } \Sigma ^ { + } - \textrm { X } ^ { 1 } \Sigma ^ { + } ( 0 , 0 ) band are measured in order to tie information from the latter emission data to the level structure of A ^ { 1 } \Pi ( v = 0 ) .
The high pressures in the absorption cell at the synchrotron and the high temperatures in the emission discharge permitted monitoring of high rotational quantum levels in A ^ { 1 } \Pi ( v = 0 ) up to J = 43 .
All information , in total over 900 spectral lines , was included in an effective-Hamiltonian analysis of the A ^ { 1 } \Pi ( v = 0 ,J ) levels that are directly perturbed by the e { } ^ { 3 } \Sigma ^ { - } ( v = 1 ) , d ^ { 3 } \Delta ( v = 4 ) , a ^ { \prime 3 } \Sigma ^ { + } ( v = 9 ) , D { } ^ { 1 } \Delta ( v = 0 ) , I { } ^ { 1 } \Sigma ^ { - } ( v = 0 , 1 ) close-lying levels and the e { } ^ { 3 } \Sigma ^ { - } ( v = 0 , 2 ) , d ^ { 3 } \Delta ( v = 3 , 5 ) , a ^ { \prime 3 } \Sigma ^ { + } ( v = 8 , 10 ) remote levels , as well being indirectly influenced by the a ^ { 3 } \Pi ( v = 10 , 11 ) state .
The influence of nine further perturber levels and their interactions was investigated and are not significant for reproducing the present experimental data .
This analysis leads to a much improved description in terms of molecular constants and interaction parameters , compared to previous studies of the same energy region for other CO isotopologues .