The spectra of the absorption coefficient (a) of GaSe a t the photon energy range 1.94 t o 2.64 eV and a t pressures between 1 bar and 12 kbar are investigated a t 295 O K . Data a t 1 t o 4360 bar confirm that the edge exciton of GaSe is the direct allowed one. The pressure coefficient of the band gap (dE,/dP = -6.2 x eV bar-I), one of the Rydberg exciton constant (dR/dP = -0.6 x eV bar-*), and one of the exciton effective massIt is supposed that two interband exciton transitions a t 2.001 and 3.25 eV give the contribution into the a spectrum above 2.1 eV. The assignment of these transitions is discussed in connection with the band structure calculation of Schluter. At 5280 bar a discontinuous jump of the absorption edge shape is observed for GaSe, with a change of t h e sign and a value for dE,/dP of +2.0 x 10-6 eV bar-' within the range of 5280 t o 11780 bar. This effect is interpreted as the transformation of one GaSe polytype into another, i.e. as a possible phase transformation close to t h a t of second kind. B HHTepBane 3~e p r~f i @oToHa OT i,94 no 2,64 eV y1 DaBneHHR OT 1 6ap no 12 kbar npH 295 O K accnenoBaHx cnempbI K O~@ @~U M~H T~ n o r n o q e~n~~ a ceneHana r a n n m GaSe. JJaHHbIe B ~n a n a a o~e OT 1 AO 4360 bar nonTsepmaamT, TO ~K C H T O H Ha KpaIo IIOrJIOIIJeHHFI GaSe RBJIReTCR IIpFIMbIM pa3peUIeHHbIM 3IECHTOHOM. npH6JIPiweHHO OIrpe~eneHbI K03@@Pi4HeHTbI HaBneHHR IUllpllHbI a a n p e q e~~o a 30HbI (dEg/dP = ---6,2 x eV -bar-I), ~C

Jointly analyAing the absorption spectra and the interference patterns in the transniission spectra of GaSe a t pressures between 1 and 5530 bar, further evidence is given rehting to polyt.ypic transformations in GaSe. namely: t.he intrapolytypic transformation when the pressure is increased from 2790 to 3350 bar and the interpolytypic transformation when thc pressure is increased from 4340 to 4710 bar. This intcrpret.ation is confirmed by the ana,lysis of the pressure dependcncc of t,he energy position of the exciton line. The possiblc mechanism of t,hcse transformations is discussed. Taking account of the intrapolytypic transformation, t,he prcssurc influence on the low-energy tail of the exciton lines is considcrccl. R cnempax npoIlycriaHtiFI GaSe B j~1 a n a 3 o~e EauJeIIMfi OT 1 110 5530 bar nonyserrbr nonomime;lbIIhie Z O K~~~T~J I~X T R~ OTHOCHTC~IHIO IIOJMTIIZIHIJX npcBpaqeirti8 B GaSe, a 3350 bar H HeHinomTmHoro rrpeuparrremfi IIPH IIoBbImeIImi xau:ieHm OT 4340 xo 4710 bar. 3~a mrTepIrpeTaqHn norrTi3epirraacTcR TaKxie a11am3ou ~~R H C M M O C T M ~H C P -n l ) M COBMeCTHOM aHajIM3e CIIeKTpOB IIOrJIOLI[eHMn M HHTCp~CpC€I~MOlIIIblX IiapTPIH MMeHJIO, B~IYTPMIIo,l~iTArIHorO IIpCBpaIIleHIIfi npI.1 nOBbIIII~HklH XaBJleHMR OT 2790 A 0 IYTIlqeCKOrO IIOJIOHieHHFI 3KCMTOHIIOfi JHHMM OT ;laBJIeHASI. 06CyiK~aeTCFI BePOSITHbIB MeXaHH3M 3TAX npeBpaILlCIIr?l~. c y9CTOM UIIYTPMIIOJIRTkIIIlIO~0 IlpeRpaII~CIIMH paCCM0-TpeHo u m m n e EauneIIHIr Ha r 1~3~o~r r e p r e~~l s e c 1~1~~ XBOCT ~KCIIIOIIZIO&~ J I M I I~I .